Cortical representations of confidence in a visual perceptual decision

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1 Received Feb Accepted Apr Publihed 5 Jun DOI:.8/ncomm9 Cortical repreentation of confidence in a viual perceptual deciion Leopold Zizlperger,, *, Thoma Sauvigny, *, Barbara Händel & Thoma Haarmeier,5 To date the exact neuronal implementation of deciion confidence ha been ubject to little reearch. Here we explore electroencephalographic correlate of human choice certainty in a viual motion dicrimination tak for either patial attention or motor effector cue intruction. We demontrate electrophyiological correlate of choice certainty that evolve a early a m after timulu onet and reemble the primary viual motion repreentation in early viual cortex. Thee correlate do not emerge unle or until the ubject unambiguouly know which of the competing viual timuli i actually relevant to behaviour. They extend beyond timulu preentation up to the motor repone but are independent of the motor effector. Our finding ugget that perceptual confidence evolve in parallel with repreentation of timulu propertie and i dedicated to one pecific apect of the viual world. It electroencephalographic correlate can be dientangled from repreentation of enory evidence, objective dicrimination performance and overt motor behaviour. Department of Neurology, RWTH Aachen Univerity, Pauweltrae, 57 Aachen, Germany. Intitute of Neurocience and Medicine, Reearch Centre Jülich GmbH, Wilhelm-Johnen-Strae, 58 Jülich, Germany. Department of Neurourgery, Univerity Medical Center Hamburg-Eppendorf, Martinitrae 5, 6 Hamburg, Germany. Ernt Strüngmann Intitute (ESI) for Neurocience in Cooperation with Max Planck Society, Deutchordentrae 6, 658 Frankfurt, Germany. 5 Cognitive Neurology, Hertie Intitute for Clinical Brain Reearch, Otfried-Müller-Strae 7, 776 Tübingen, Germany. * Thee author contributed equally to thi work. Correpondence and requet for material hould be addreed to T.H. ( thoma.haarmeier@uni-tuebingen.de). NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

2 NATURE COMMUNICATIONS DOI:.8/ncomm9 Natural perceptual ytem have to cope with ytematic uncertainty a enory information i noiy and inufficient to uniquely determine the environment. Accordingly, viual perception ha been decribed a a proce of inference by which ambiguou enory cue are combined with internal knowledge of the world to arrive at a conitent interpretation of the cene,. The Bayeian tatitical theory frame thi problem quantitatively and ha been uccefully applied to cognitive phenomena in perception, and enorimotor learning 5,6. To optimize behaviour a per the Baye rule, ubjective certaintie reflecting non-dichotomou conditional probabilitie 7 of both previou knowledge and enory input determine their optimal weighting in every perceptual deciion. Neuronal recording in behaving monkey 7,8 and rat 9 have detected repreentation of deciion formation and the degree of certainty in it. For perceptual deciion uch a a monkey dicrimination of viual motion direction in a noiy random dot diplay and reporting it by an eye movement neural correlate have been demontrated in a enorimotor aociation area that i concerned with the preparation of the action. When monkey report the perceived direction of viual motion by a accadic eye movement, lateral intraparietal cortex (LIP) neuron repreent the accumulation of evidence 8 a well a choice certainty 7. Thi pool of neuron gradually increae or decreae it firing rate a more evidence mount for or againt one of the choice; LIP neuron utain a dicharge that determine the outcome of the deciion when the accumulated evidence reache a critical level. The exact neurobiology underlying the negotiation of thi threhold and the underlying evidence i not currently known. Yet theoretical and experimental data ugget that the neural computation approximate a form of probabilitic reaoning featuring choice certainty,7,. Surpriingly, to date there i little electrophyiological evidence on human choice certainty.ina recent pychophyical tudy, we invetigated the influence of patial and feature-baed attention on human choice certainty uing a motion dicrimination tak and a certainty wager imilar to a pioneering experiment in behaving monkey 7. Complemented by numerical confidence rating, our data revealed a diociation of choice accuracy and certainty with a ignificantly tronger influence of voluntary top-down attention on ubjective performance meaure than on objective performance. Selective attention i capable of diociating a perceptual deciion and the confidence in it by affecting them differently. In the electroencephalographic (EEG) experiment preented here, we ought to characterize the electrophyiological ignature of human choice certainty and further clarify the role of thi metacognitive evaluation in motor preparation. Since in nonhuman primate choice certainty i encoded by the ame population of neuron a the perceptual deciion and the accadic eye movement indicating the direction deciion 7,8, we here eparated perceptual integration and motor planning by requeting ubject to report their deciion by hand movement in delayed-repone paradigm. To diociate phyiological repreentation of objective performance and ubjective confidence even further, in a firt experiment we aked one group of ubject to indicate the perceived direction of moving random dot and the confidence in that perceptual deciion while timuli were cued validly and invalidly. In the econd experiment, we did not cue elective attention but the motor effector to identify electrophyiological correlate of deciion confidence in motor preparation. Our finding ugget that perceptual confidence evolve in parallel with repreentation of timulu propertie and i dedicated to pecific apect of viual timuli. Reult Experiment. While -channel EEG wa recorded, in the firt experiment we let human ubject dicriminate global viual motion embedded in noie for validly and invalidly cued timuli (Fig. a) and rate the confidence in their perceptual deciion. Both four-alternative forced choice repone were acquired trial by trial. Subject oberved two random dot kinematogram (RDK) preented imultaneouly in their left and right viual hemifield. While a precue indicated which RDK to attend to with 8% validity, participant did not know definitely which one of the two would prove behaviourally relevant until potcue onet following timulu preentation. Subject indicated the direction of perceived global viual motion uing their right hand via a firt button pre (up, down, left or right), by the following button pre they rated their confidence on a cale of ( being I gueed, I wa ure ). Objective and ubjective performance meaure. Reflecting the dependency of tak difficulty on motion coherence, dicrimination performance increaed for higher motion coherence in both attention condition a expected,. Furthermore, we found higher enitivity to viual motion for valid a compared with invalid cue a indicated by higher mean accuracy with attention for each of the four coherence level (mean accuracy for /// % coherence, valid cue:.5/.77/.87/.9; invalid cue:./.6/.75/.8; Fig. c). That i, for a given coherence level attention increaed the proportion of correct choice. Thi improvement in performance for an attended timulu i the ignature of attentional modulation on behaviour 5 and demontrate that ubject reliably followed the cue intruction. Deciion confidence a expreed by a certainty index (ee Method for detail) varied with cueing condition, a well: potdeciion certainty for valid cue trial wa ignificantly higher than for invalid cue trial (mean certainty index:.6 veru.; t-tet: Po.), certainty indice for valid and invalid cue differed ignificantly for all four coherence level (t-tet for all contrat: Pr.). Similar to the effect in objective performance, certainty indice increaed with higher motion coherence (mean certainty index for ///% coherence, valid cue:.8/.7/.8/.86; invalid cue:.9/.5/.6/.7; Fig. d). There wa a ignificant difference between certainty indice of all four coherence level for valid and invalid cue eparately (t-tet for all contrat: Pr.). Accordingly, mean motion coherence underlying the highet certainty rating wa ignificantly higher than mean motion coherence underlying the lowet certainty rating for both cueing condition (valid cue:.9% veru 7.%, t-tet: Po.; invalid cue:.8% veru 9.%, t-tet: Po.). Increae of mean confidence with attention were more pronounced than for choice accuracy. Thi indicate an even tronger effect of elective attention on potdeciion certainty a compared with choice accuracy. To quantify and further invetigate thi attention-related variation, every ubject mean accuracy and certainty of the four coherence level each for valid and invalid cue were z-tranformed to a common mean () and.d. (). In accordance with our previou tudy, paired t-tet on thee tandardized meaure revealed not only ignificant increae for deciion accuracy and choice confidence with attention (both t-tet: Po.; Fig. e, poitive D z-value for each category), but alo a ignificantly tronger increae of the confidence meaure (t-tet: P ¼.; labelled grey in Fig. e). Similarly, repone time (RT) varied with timulu propertie. Following the offet of the econd arrow (.5 ), ubject would indicate the direction of coherent motion and their choice certainty. RT were ignificantly fater in valid cue trial (valid: mean ¼.±.9 ; invalid: mean ¼.58±.8 ; t-tet: NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

3 ARTICLE NATURE COMMUNICATIONS DOI:.8/ncomm9 Po.). Both in valid and invalid cue trial, repone were ignificantly fater for correct motion dicrimination (valid: mean correct ¼.±.5, mean incorrect ¼.6±.68 ; t-tet: Po.; invalid: mean correct ¼.99±.79, mean incorrect ¼.56±.9 ; t-tet: Po.). Subject were fater to repond to higher coherence level with a ignificant difference of highet and lowet coherence for valid cue (valid: mean for % coherence ¼.8±.5, mean % ¼.6±. ; t-tet: P ¼.6; invalid: mean % ¼.±., mean % ¼.6±.6 ; t-tet: P ¼.8). RT were fater with higher choice certainty with ignificant difference between highet and lowet confidence level for both cueing condition (valid: mean for certainty ¼.95±., mean ¼.±.7 ; t-tet: P ¼.8; invalid: mean ¼.5±.5, mean ¼.59±. ; t-tet: Po.). Electrophyiological correlate of deciion confidence. Figure a uperimpoe the grand-average event-related potential (ERP) of the ubject four certainty level time-locked to.5 the onet of the trial. A chematic of the behavioural tak equence i diplayed along with the coure of the ERP. Following the appearance of the precue at.5 and potcue arrow at. a well a following RDK onet at. and offet at., we oberved ditinctive viual-evoked potential. In that all EEG electrode were referenced to FCz, the firt prominent deflection after each of thee four point in time at about m conformed to common viual N effect, the econd at about 5 m to P effect. A further peak oberved at around m after the potcue wa identified to repreent a claical P effect (ee for example, polarity of ERP component in exemplary grandaverage ERP for valid and invalid trial referenced to linked matoid in Fig. ). Averaged acro certainty rating, ERP revealed two pronounced diociation of brain electrical activity that differed in polarity and localization. With increaing potdeciion certainty, we oberved monotonically increaing negative potential hift during the preentation of the tet timulu (.5 to. ) and acendingly poitive potential hift about m after the onet of the repone window at.5 (red arrow in Fig. a). In a tatitical comparion of lowet and highet certainty Attentional cue. Pretimulu..5 Tet timulu.5 Pretimulu Tet timulu.. Action cue Right hand. Left hand.5 Intructional cue Valid (8%). Invalid (%) c a e c r c t Motion coherence (%) Proportion correct / certainty index Motion coherence (%) Valid cue.8 Invalid cue.6.. P =. Valid cue Invalid cue Δ z-value Certainty index Proportion correct Accuracy.8 Certainty Motion coherence (%) Figure Tak deign and behavioural data for Experiment and. (a) Experiment : timing of event for an example trial: the tet timulu conited of two random dot kinematogram (RDK) preented imultaneouly left and right of the fixation point (.5 ), level of motion coherence and direction of global motion (four alternative) wa modulated on a trial-by-trial bai. An arrow before timulu preentation (.5 ) indicated which RDK covertly hift attention to, a econd arrow after the timulu (.5 ) intructed ubject which RDK they actually had to report the direction of coherent motion for. Valid cueing of patial elective attention a defined by congruent orientation of the attentional and the intructional cue wa applied in 8% of trial, ee dark blue option. Invalid cueing (incongruent arrow, light blue option) wa applied in the remaining % of trial. Subject reported perceived motion direction with a firt button pre and deciion certainty with either a econd pre of the ame button uing four predefined numerical rating. (b) Experiment : thi light variation involved no cueing of elective attention, but an intruction a to which hand to repond with. Timing of event correponded to a, but the attentional cue (.5 ) wa ubtituted by an extended fixation period. Pretimulu and tet timulu were randomly preented in the left or right viual hemifield, and intead of the potcue (.5 ) an action cue wa preented intructing ubject randomly a to which hand to repond with. (c) Experiment, proportion of correct repone for the four motion coherence level and the two cueing condition eparately, all ubject. (d) Experiment, certainty index for the four motion coherence level and the two cueing condition eparately, all ubject. (e) Experiment, elective attention increaed both z-tandardized proportion of correct repone (accuracy) and certainty a indicated by poitive z-value, all ubject. Certainty increaed ignificantly more with attention than accuracy (t-tet: P ¼.). (f) Experiment, proportion of correct repone and certainty index for the four motion coherence level, all ubject. All bar chart diplay mean±.e.m. NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

4 NATURE COMMUNICATIONS DOI:.8/ncomm9 valid cue invalid Choice cue certainty / / / C,P,P,O,O,Cz,Pz,CP,CP,CP Choice certainty veru Figure Difference between confidence rating in Experiment. (a) Symbolic repreentation of the viual timulu along the timulu-locked grandaverage event-related potential (ERP) repone. Different colour repreent ERP for the four different confidence rating, on a cale of (from being I gueed, to I wa ure ). (b) Stimulu-locked grand-average ERP repone to highet veru lowet confidence rating differed in two time interval (indicated by pink area). Headplot of the nonparametric cluter-randomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of I wa ure veru I gueed rating from.77 to.98 (negative cluter; P ¼.) and from.7 to.8 (poitive cluter; Po.). Heat colour of the map repreent the t-value of the tatitical comparion (colour bar indicate t-value, relative caling i pecific to each topoplot) and the black circle repreent electrode that contribute to the ignificant cluter. ERP repone are average over all electrode that were part of the late ignificant cluter and are plotted with.e. value of the mean in b (haded area). The ERP dicontinuity around. indicate an artefact due to the ynchronization pule of EEG and preentation computer. Valid veru invalid cue C,P,P,O,O,Cz,Pz,CP,CP,CP Figure Linked-matoid grand-average ERP repone to valid cue and invalid cue trial in Experiment. Valid cue were preented in 8% of the trial, hence for the infrequent invalid cue about m after the potcue (potcue tart time:. ) a claical P component wa oberved. ERP repone are average over electrode C, P, P, O, O, Cz, Pz, CP, CP, CP6 and are plotted with.e. value of the mean (haded area). The ERP dicontinuity around. indicate an artefact due to the ynchronization pule of EEG and preentation computer. trial (Fig. b), thee component were expreed by a ignificant negative cluter (P ¼.) over parieto-occipital electrode that wa preent from.77 to.98 and a large, ignificant poitive cluter (Po.) from.7 to.8. Do factor that covary with confidence like motion coherence and attention contribute to the effect een here? Firt, choice certainty wa inpected for valid and invalid cue trial eparately. A timuli were not varied ytematically until the tet timulu tarted, the following ERP are plotted tarting at around.5. Contrating the four confidence ERP of valid cue (Fig. a) with the repective ERP of invalid cue (Fig. b), the early diociation during tet timulu preentation perited for both cueing condition. For highet veru lowet certainty, thi difference wa expreed by a ignificant negative cluter from.7 to.9 in valid (P ¼.; Fig. e) and from.765 to.87 in invalid cue trial (P ¼.5; Fig. g). The econd ignificant diociation een in the pooled data above, however, wa oberved for valid cue trial only. It wa expreed by a ignificant poitive cluter (P ¼.) of parieto-occipital electrode (Fig. f) that wa preent from.7 to.8. By analying the ERP for the two cueing condition eparately, the influence of invalid cueing could be determined a well. A expected, viual inpection howed nearly congruent waveform up to the preentation of the econd arrow defining the cueing condition at.. Two negative hift peaking at about and 5 m, repectively, after the potcue were oberved, the econd one for invalid cue trial only. We conider the firt deflection to be a P component a mentioned above, the econd for the % of all trial with incongruent potcue a claical P component. For invalid cue trial, P amplitude ignificantly increaed with choice certainty a expreed by a large negative cluter (P ¼.) that wa preent from.6 to.6 and wa pronounced over the right hemiphere (Fig. h). In ditribution and polarity, thi increae very much reembled the one oberved for the diociation of certainty ERP during tet timulu preentation in both valid and invalid cue trial (ee for example, Fig. e,g). The difference between the highet and lowet certainty rating jut mied ignificance for the P component. Mean motion coherence wa higher in more certain repone: 6.96% for certainty rating, 9.% for,.5% for,.9% for in valid and 9.% for,.7% for, 8.% for,.85% for in invalid cue. Therefore, ERP difference een for the different certainty level during tet timulu preentation could baically be explained by underlying motion coherence. To tet whether difference in ERP oberved for the different certainty level (Fig and ) are econdary to difference induced by viual timulation, we alo examined the impact of the preented motion coherence on the effect oberved for choice certainty and cueing condition. Figure 5 ide-by-ide diplay the ERP for the four motion coherence level,,, and % preented in the experiment. For valid (Fig. 5a) and invalid cue alike (Fig. 5b), with increaing motion coherence the onet of the coherent motion ignal at.5 elicited monotonically increaing negative potential hift. Cluter-level randomization tet identified a larger negative deflection over parieto-occipital electrode for % motion coherence a compared with % coherence from.7 to.95 in valid (Fig. 5e) and from.67 NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

5 NATURE COMMUNICATIONS DOI:.8/ncomm9 ARTICLE Choice certainty / / /, valid cue C,C,P,P,O,O,Pz,CP,CP,CP5,CP Choice certainty / / /, invalid cue C,C,P,P,O,O,Pz,CP,CP,CP5,CP e Choice certainty veru, valid cue f g h Choice certainty veru, invalid cue Figure Difference between confidence rating in Experiment for valid cue and invalid cue trial. (a,b) Stimulu-locked grand-average certainty ERP repone to valid cue (a) and invalid cue trial (b). Different colour repreent ERP for the four different confidence rating, on a cale of (from being I gueed, to I wa ure ). (c,d) Stimulu-locked grand-average ERP repone to highet veru lowet confidence rating in valid cue (c) and invalid cue trial (d) differed in four time interval (indicated by pink area). (e h) Headplot of the nonparametric cluter-randomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of I wa ure veru I gueed rating. Heat colour of the map repreent the t-value of the tatitical comparion (colour bar indicate t-value, relative caling i pecific to each topoplot) and the black circle repreent electrode that contribute to the ignificant cluter. (e) Negative cluter from.7 to.9 in valid cue trial (P ¼.). (f) Poitive cluter from.7 to.8 in valid cue trial (P ¼.). (g) Negative cluter from.765 to.87 in invalid cue trial (P ¼.5). (h) Negative cluter from.6 to.6 in invalid cue trial (P ¼.). ERP repone are average over all electrode that were part of the late ignificant cluter in valid cue trial (f) and are plotted with tandard error of the mean in c,d (haded area). to.888 in invalid trial (Fig. 5f). Interetingly, a imilar ERP diociation wa alo oberved later in the coure of the trial, thi time for invalid cue only. For invalid a oppoed to valid cue, the two prominent potential component following potcue onet at. were coherence-dependent, a well (negative deflection between. and.5 diplayed in Fig. 5b). We oberved potential hift to be in invere proportion to the four preented motion coherence. Cluter tatitic exemplarily highlighted larger negative deflection over parieto-occipital electrode from.8 to.5 (P ¼.8; Fig. 5g) and from. to. (P ¼.8; Fig. 5h) for % a compared with % coherence. Thu, both the P and the P component varied with preented motion coherence, and thi motion dependence for invalid cue wa imilar in polarity and ditribution to the earlier repone een during the preentation of the motion timulu for both cueing condition. While cluter-level randomization tet identified ignificant difference between ERP of different coherence level during the B5 m preceding timulu offet for valid and invalid cue alike (Fig. 5e,f), they did not for the time interval of the late certainty diociation. Thi finding uggeted that the early certainty correlate poibly i confounded by timulu characteritic, the late diociation with deciion confidence, by contrat, i not. To further ubtantiate our concluion, we examined grandaverage ERP of highet veru lowet confidence rating in valid cue trial for correct anwer (Fig. 6a), for a ingle coherence level only (% motion coherence; Fig. 6b) and for the overlap of thee two election of trial (Fig. 6c). The late, ignificant diociation NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 5 & Macmillan Publiher Limited. All right reerved.

6 NATURE COMMUNICATIONS DOI:.8/ncomm9 % % % % motion coherence, valid cue P,P,O,O,Pz,CP,CP % % % % motion coherence, invalid cue P,P,O,O,Pz,CP,CP e % % motion coherence, valid cue f g h % % motion coherence, invalid cue Figure 5 Difference between preented motion coherence level in Experiment for valid cue and invalid cue trial. (a,b) Stimulu-locked grandaverage coherence ERP repone to valid cue (a) and invalid cue trial (b). Different colour repreent ERP for the four different level of motion coherence (,, and %) preented in the experiment. (c,d) Stimulu-locked grand-average ERP repone to the highet and the lowet coherence level in valid cue (c) and invalid cue trial (d) differed in four time interval (indicated by pink area). (e h) Headplot of the nonparametric cluterrandomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of veru % motion coherence. Same convention a in Fig., colour bar indicate t-value, relative caling i pecific to each topoplot. (e) Negative cluter from.7 to.95 in valid cue trial (P ¼.). (f) Negative cluter from.67 to.888 in invalid cue trial (Po.). (g) Negative cluter from.8 to.5 in invalid cue trial (P ¼.8). (h) Negative cluter from. to. in invalid cue trial (P ¼.8). ERP repone are average over electrode P, P, O, O, Pz, CP, CP and are plotted with.e. value of the mean in c,d (haded area). een in the pooled data above wa oberved imilarly for all three additional analye. Each diociation wa expreed by a ignificant poitive cluter of parieto-occipital electrode with imilar temporal characteritic (ee for example, Fig. 6d f veru Fig. f). Thee variation of a late, ignificant ERP difference were oberved over left-parietal electrode and preceded the mean repone time for the highet and lowet certainty level (.79, valid cue only) by about m. A all ubject reponded with their right hand, thi finding uggeted an aociation with the motor repone. With a ignificant difference between repone time for highet and lowet certainty in valid cue (mean RT for highet certainty.95 veru lowet. ; t-tet: P ¼.8), in the final tep of thi analyi we examined motor preparation more cloely. Figure 6g diplay grand-average certainty ERP repone-locked to the firt button pre. ERP did not how relevant activity for each of the two certainty level within the m before button pre. Cluter tatitic did not reveal a ignificant difference between the two grand average indicating that there i no certainty-pecific activity time-locked to the repone. Experiment. In the econd experiment a ingle RDK wa preented in either the left or the right viual hemifield without elective patial attention cueing, rather ubject were intructed a to which hand to repond with trial by trial (Fig. b). Similar to the firt experiment, ubject would not be able to prepare a motor repone until action cue onet, even though the behaviourally relevant viual timulu wa evident right from RDK onet. A in Experiment, dicrimination performance increaed 6 NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

7 NATURE COMMUNICATIONS DOI:.8/ncomm9 ARTICLE Choice certainty veru, valid cue, correct repone.5..5 Choice certainty veru, valid cue, % coherence d C,P,P,O,O,T7, P7,P8,Pz,CP5,CP6.5 e C,P,P,O,T7,Pz, CP,CP,CP5,CP6.5 f.. Choice certainty veru, valid cue, % coherence, correct repone P,T7, CP,CP5. 5 Repone Choice certainty veru, valid cue C,C,P,P,O,O,Pz,CP,CP,CP5,CP6.... Figure 6 Certainty correlate for Experiment. (a c) Stimulu-locked grand-average ERP repone to highet veru lowet confidence rating in valid cue trial: (a) for correct repone only, (b) for a ingle level of preented motion coherence (% of coherently moving dot in both tet timulu dotfield), (c) for correct repone in % motion coherence trial. Pleae note that with more retrictive election criteria from a to c the ize of the repective pool of trial decreaed coniderably. Each of the three ERP contrat (a c) differed in a imilar time interval (indicated by pink area). (d f) Headplot of the nonparametric cluter-randomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of I wa ure veru I gueed rating. Heat colour of the map repreent the t-value of the tatitical comparion (colour bar indicate t-value, relative caling i pecific to each topoplot) and the black circle repreent electrode that contribute to the ignificant cluter. (d) Poitive cluter (P ¼.7) from.76 to.88 for correct repone in valid cue trial. (e) Poitive cluter (P ¼.) from.79 to.8 for % motion coherence in valid cue trial. (f) Poitive cluter (P ¼.) from.768 to.89 for correct repone in valid cue % motion coherence trial. (g) Stimulu-locked grand-average ERP repone to highet veru lowet confidence rating in valid cue trial. Pleae note that both point of reference and time caling differ from previou ERP plot a it zoom in on the 5 m before the dicrimination repone (firt button pre; red line). No relevant activity wa detected in the average during the time interval preceding the motor repone. Cluter tatitic did not reveal a ignificant difference between highet and lowet confidence rating of valid cue trial for repone-locked ERP repone. ERP repone are average over all electrode that were part of the repective ignificant cluter and are plotted with.e. value of the mean (haded area). for higher motion coherence (mean accuracy for 5/5//7% coherence:.5/.55/.8/.9), a did deciion confidence (mean certainty index for 5/5//7% coherence:./.5/.7/.9; Fig. f). RT varied with timulu propertie: repone were ignificantly fater for correct motion dicrimination (mean correct ¼.75±.8, mean incorrect ¼.99±.89 ; t-tet: P ¼.). Subject were fater to repond to higher coherence level with a ignificant difference of highet and lowet coherence (mean for 7% coherence ¼.5±.8, mean 5% ¼.79±.96 ; t-tet: P ¼.). RT were fater with higher choice certainty, with ignificant difference between highet and lowet confidence level (mean for certainty NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 7 & Macmillan Publiher Limited. All right reerved.

8 NATURE COMMUNICATIONS DOI:.8/ncomm9 C/,P/,O/,T7/8,P7/8,Cz,Pz, Choice certainty / / / FC/,CP/,FC5/6,CP5/6,TP9/ c d e f g Choice certainty veru Figure 7 Difference between confidence rating in Experiment. (a) Symbolic repreentation of the viual timulu along the timulu-locked grandaverage ERP repone. Different colour repreent ERP for the four different confidence rating, on a cale of (from being I gueed, to I wa ure ). (b) Stimulu-locked grand-average ERP repone to highet and lowet confidence rating differed in five time interval (indicated by pink area). (c g) Headplot of the nonparametric cluter-randomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of I wa ure veru I gueed rating. Heat colour of the map repreent the t-value of the tatitical comparion (colour bar indicate t-value, relative caling i pecific to each topoplot) and the black circle repreent electrode that contribute to the ignificant cluter. (c) Negative cluter from.7 to.9 (P ¼.). (d) Poitive cluter from.5 to. (Po.). (e) Negative cluter from.7 to. (P ¼.). (f) Negative cluter from.7 to.7 (P ¼.). (g) Poitive cluter from.68 to.78 (P ¼.9). ERP repone are average over all electrode of cluter (d) and are plotted with.e. value of the mean (haded area). ¼.±.6, mean ¼.6±.66 ; t-tet: P ¼.). Figure 7a overlay the grand-average event-related potential (ERP) of the ubject four certainty level time-locked to the onet of the trial. With the omiion of the elective attention intruction of Experiment, ERP changed coniderably. While pretimulu RDK onet at. and the appearance of the action cue at. evoked claical N and P effect (ee for example, Experiment ), we oberved five pronounced diociation of brain electrical activity with different polaritie and localization. In a tatitical comparion of lowet and highet certainty trial (Fig. 7b), thee diociation were expreed by three ignificant negative cluter over parieto-occipital electrode that were preent from.7 to.9 (P ¼.),.7 to. (P ¼.), and.7 to.7 (P ¼.); a well a by two poitive cluter from.5 to. (Po.; electrode plotted in ERP) and.68 to.78 (P ¼.9). Conitent with the control in Experiment, in the econd experiment we inpected the contrat of lowet and highet certainty trial for the influence of the preented motion coherence. Figure 8a ide-byide diplay the ERP for the four motion coherence level 5, 5, and 7% preented in Experiment and the reult of the cluter tatitic. Randomization tet identified larger negative deflection over parieto-occipital electrode for 7% motion coherence a compared with 5% coherence from.66 to.89 (P ¼.7) and from.58 to.97 (P ¼.5); a well a a larger poitive deflection for thi contrat from.96 to.8 (Po.; electrode plotted in ERP). Higher motion coherence in more certain repone.88% for certainty rating, 7.7% for,.8% for, 5.59% for could account for the early certainty ERP difference, but could not for the ERP diociation after the action cue (ee for example, Fig 7b and 8b). Again, that motivated further control for covariance of certainty with further timulu propertie or ubject performance. We firt inpected ERP of highet veru lowet confidence rating for correct anwer (Fig. 9a). In a next tep, we examined the certainty contrat for a combined grand average of ingle ubject 5 and % motion coherence average a there were not enough high certainty trial for the 5% coherence level and not enough low certainty trial for the % coherence level to generate eparate average that were adequate for cluter tatitic (Fig. 9b). While the ignificant ERP diociation are marked for all pool of trial, to avoid redundancy the topography of the ignificant cluter i jut detailed for the mot rigorou of the control that i the interection of thee two pool of trial (Fig. 9c). In contrat to Experiment, the early diociation during timulu preentation proved ignificant for all three pool of trial, mot notably for the two coherence control in Fig. 9b,c, a well. Thi certainty correlate wa repreented by a ignificant negative cluter from.8 to.85 (P ¼.). During the interval leading from timulu offet to the action cue ERP difference were expreed by two ignificant poitive cluter from.6 to.9 (P ¼.9) and from. to.55 (P ¼.9), repectively, a well a two ignificant negative cluter from.89 to.95 (P ¼.9) and from.8 to. (P ¼.). All five ERP activation indicative of choice certainty, thu, were not confounded by the preented motion coherence. The late, ignificant diociation een in the pooled data above (Fig. 7g) wa detected for the econd control only (Fig. 9j) but 8 NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

9 NATURE COMMUNICATIONS DOI:.8/ncomm9 ARTICLE a C/,P/,O/,T7/8,P7/8,Cz,Pz,FC/,CP/,FC5/6,CP5/6 b 5% 5% % 7% motion coherence c d e. 5% 7% motion coherence c d e Figure 8 Difference between preented motion coherence level in Experiment. (a) Stimulu-locked grand-average coherence ERP repone. Different colour repreent ERP for the four different level of motion coherence (5, 5, and 7%) preented in the experiment. (b) Stimulu-locked grand-average ERP repone to the highet and the lowet coherence level differed in three time interval (indicated by pink area). (c e) Headplot of the nonparametric cluter-randomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of 7 veru 5% motion coherence. Same convention a in Fig., colour bar indicate t-value, relative caling i pecific to each topoplot. (c) Negative cluter from.66 to.89 (P ¼.7). (d) Poitive cluter from.96 to.8 (Po.). (e) Negative cluter from.58 to.97 (P ¼.5). ERP repone are average over electrode of cluter (d) and are plotted with.e. value of the mean (haded area) in b. mied ignificance in the other two control. It wa expreed by a ignificant poitive cluter of parieto-occipital electrode from.7 to.775 (P ¼.). Again, we found a ignificant difference between repone time for highet and lowet certainty (mean RT for highet certainty.8 veru lowet.9 ; t-tet: P ¼.). Thi difference wa alo ignificant when left hand (.7 veru. ; t-tet: P ¼.) and right hand repone (.87 veru. ; t-tet: Po.) were analyed eparately. A tatitical comparion of confidence-pecific ERP activity (D certainty ) did not how a ignificant difference between right and left hand repone (Fig. 9d). Thi control demontrated that correlate of choice certainty did not depend on the motor effector. Dicuion The preent tudy wa performed to ytematically manipulate the level of elective attention and motor effector, and relate both to objective performance and ubjective confidence a well a to electrophyiological correlate of viual perceptual certainty. Conitent with previou tudie,6 deciion confidence correlated with different experimental variable, that i, enory evidence, elective attention and motor repone time a expected. We performed trict control to etablih pecific correlate of choice certainty not confounded by thee covariance. Indeed, ERP variation with motion coherence and patial cueing could have been mitaken for primary repreentation of deciion confidence. Viual-evoked ERP activity tarted to differ ignificantly between the four level of motion coherence a early a B7 m after timulu onet (Fig. 5f). The cortical activity that gave rie to thi effect and linearly increaed with motion coherence i likely to reflect compound activitiy of large part of motion enitive viual cortex including, among other, area MT/MST, VA, and alo parietal cortex (ee for example, Fig, and 5). Neuron in area MT have been hown to linearly increae firing rate with motion coherence in variou ingle-cell recording tudie 7,8 and the trength of viual motion i reflected in human area MT þ activity in fmri 9, MEG and EEG data. Interetingly, the evoked activity following invalid potcue in our Experiment alo varied with attribute of the viual timulu, that i, motion coherence (Fig. 5g). It patial ditribution very much reembled the early viual-evoked potential reflecting motion trength (Fig. 5f). Thi ugget that part of the motion-enitive cortex were reactivated following invalid potcue, even though the viual motion timulu wa not repeated. In other word, invalid cueing apparently induced a retrieval of motion information from working memory finally reulting in the perceptual deciion. A claic P potential following the le frequent invalid cue varied with motion coherence, a well (Fig. 5h). While the exact mechanim underlying perceptual deciion in invalid cue trial were not within the cope of our experiment, the tatitical comparion confined to a ingle coherence level or attention condition allowed u to decide on whether a poible ERP correlate of choice certainty wa econdary to timulu propertie or attentional tate. Following that approach, our finding revealed a equence of ERP repone indicative of ubjective confidence. The firt certainty correlate wa oberved during the preentation of the tet timulu. Capitalizing on the EEG high temporal preciion, our data let u determine when perceptual confidence form NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 9 & Macmillan Publiher Limited. All right reerved.

10 NATURE COMMUNICATIONS DOI:.8/ncomm9 a C/,P/,O/,T7/8,P7/8,Cz,Pz,FC/,CP/,FC5/6,CP5/6 b c d 5 Choice certainty veru, correct repone C/,P/,O/,F7,T7/8,P7/8,Cz,Pz,CP/,FC5/6,CP5/6,TP9/ C j Choice certainty veru, 5% and % coherence C/,P/,O/,F7/8,T7/8,P7/8,Cz,Pz,CP/,FC5,CP5/6,TP9/ FC / e f g h i Choice certainty veru, 5% and % coherence, correct repone P,P,O,O,Pz,CP,CP Δ Choice certainty, left veru right hand e f g h i j Figure 9 Certainty correlate for Experiment. (a c) Stimulu-locked grand-average ERP repone to highet veru lowet confidence rating: (a) for correct repone only, (b) for an average of 5 and % motion coherence, (c) for correct repone in 5 and % motion coherence trial. Each of the three ERP contrat (a c) differed in rather imilar time interval (indicated by pink area). Pleae note that with more retrictive election criteria from a to c the ize of the repective pool of trial decreaed coniderably. (d) Stimulu-locked ERP of certainty-pecific activity (D choice certainty ) for left veru right hand repone. Cluter tatitic in d did not reveal a ignificant diociation of D choice certainty ERP for left veru right hand repone. (e j) Headplot of the nonparametric cluter-randomization approach (two-tailed t-tet, corrected for multiple comparion at a cluter-level, Po.5) map the calp ditribution of tatitical difference of I wa ure veru I gueed rating. Heat colour of the map repreent the t-value of the tatitical comparion (colour bar indicate t-value, relative caling i pecific to each topoplot) and the black circle repreent electrode that contribute to the ignificant cluter. While the ignificant ERP diociation are marked for all three pool of trial, to avoid redundancy the topography of the ignificant cluter i jut detailed for the mot rigorou of the control that i the interection of thee two pool of trial (c). (e) Negative cluter from.8 to.85 (P ¼.). (f) Poitive cluter from.6 to.9 (P ¼.9). (g) Poitive cluter from. to.55 (P ¼.9). (h) Negative cluter from.89 to.95 (P ¼.9). (i) Negative cluter from.8 to. (P ¼.). (j) Poitive cluter from.7 to.775 (P ¼.). ERP repone are average over all electrode that were part of the repective ignificant cluter and are plotted with.e. value of the mean (haded area). NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

11 NATURE COMMUNICATIONS DOI:.8/ncomm9 ARTICLE in the viual pathway. In Experiment, certainty-pecific ERP activity, independent of the preented motion coherence, followed timulu onet by B m (Fig. 9c). Correlate of perceived confidence thu emerged B m later than repreentation of motion coherence that followed timulu onet by B7 m (ee for example, Fig. 9c veru Fig 5c,d and 8b). Perceptual deciion confidence thu evolved nearly in parallel with repreentation of timulu propertie. The ditribution of thi early certaintypecific ERP activity wa very imilar to the cortical topography of the enory evidence uggeting a hared neurophyiological ubtrate. Subequent ditinct correlate of perceived confidence were identified during the, m leading to the action cue (Fig. 9f h). Thee certainty correlate in the EEG ignal during the fixation period between RDK offet and action cue onet were enhanced over parieto-occipital electrode, a well, and changed polarity once during the, m interval. In contrat to Experiment, Fig. 7b diplay certainty-pecific ERP activity during timulu preentation in the econd experiment, and later anew during the following fixation, that i not confounded by enory evidence or objective dicrimination performance (ee for example Fig. 9a c). Moreover, by keeping the ignal-to-noie ratio contant (Fig 6b and 9b) we illutrated that the certainty correlate were not confounded by a tak-difficulty component or noie-induced modulation of enory proceing demand. Both experiment, however, revealed an electrophyiological correlate of deciion confidence during the time interval leading from the potcue in Experiment or action cue in Experiment, repectively, to the motor repone. Thi correlate wa not confounded by timulu or repone characteritic either (ee for example Fig 6a c and 9b). Why did the two perceptual tak differ with repect to the certainty-pecific ERP activity detected in the coure of the experiment? We tarted our dicuion with Experiment that featured a lightly impler experimental deign. Mot notably, it did not include attention cueing, but randomly varied the intruction a to which effector (right or left hand) to ue for the motor repone. In Experiment, ERP time-locked to the viual timulu howed ignificant difference in brain electrical activity with deciion confidence for pooled data (Fig. ) and eparate cueing condition alike (Fig. ). But in contrat to Experiment, control for the influence of preented motion coherence demontrated that it wa more parimoniou to aume that the correlation of thi ERP component with certainty wa due to it covariance with preented motion coherence (Fig. 6). Since mean motion coherence wa higher in more certain repone, ERP difference een in Experiment for the different certainty level during tet timulu preentation thu could be explained mot parimoniouly by electrophyiological correlate of viual motion proceing, that i, by difference in enory evidence. While thi wa alo true for the early part of the certainty correlate during timulu preentation in Experiment, we oberved ditinct correlate of perceived confidence emerging about B m later than repreentation of motion coherence that followed timulu onet by B7 m (ee for example, Fig. 9c). The ubequent certainty-pecific activation during the, m after timulu offet were not preent at all in Experiment. A the coure of the two experiment i imilar except for attention cueing, we propoe that choice certainty doe not evolve unle or until deciion variable are unambiguou. Although timuli were cued validly in 8% of the trial in Experiment, obviouly ubject would not attribute certainty to one of the two random dot timuli until the intructional potcue clearly indicated which of the two wa relevant to behaviour. Confidence thu appear to form only if the target of interet i unambiguou. Thi obervation ugget that perceptual confidence like the deciion proce itelf i unitary and aigned to one pecific apect of the viual world but not hared acro different item. Then again, thi perpective implie that ubject were not able to completely ignore the ditractor timulu, even though their behavioural data how that they followed the attention intruction. Apparently ubject to ome extent divided their patial attention a mode of behaviour controverially debated in the previou literature 5,6 or hifted patial attention in time. The latet of the certainty correlate in the coure of the firt experiment appeared in valid cue trial only (ee for example, Fig. c veru Fig. d). The onet of the ignificant confidencepecific cluter (Fig. 6d f) preceded the motor repone by about m relating to the mean repone time of highet and lowet confidence rating. In that all our ubject indicated perceived motion direction by finger movement of their right hand in Experiment, thi activity focu over left parietal cortex motivated further control for the potential confounder of motor contribution to the repone. A mean repone time for highet and lowet certainty rating differed ignificantly, we aligned the ERP to the repone (firt button pre) to control for the potential confounder of motor contribution to the repone (Fig. 6g). ERP did not how relevant certainty-pecific activity time-locked to the repone within the m preceding the button pre. To comprehenively elucidate the poible role of choice certainty in motion preparation, Experiment did not include attention cueing, but randomly varied the intruction a to which motor effector to ue for the repone. The late ERP repone oberved for valid trial in Experiment wa replicated in the econd experiment with very imilar temporal and patial characteritic (Fig 7g and 9j). The deign of the econd tak made a comparion of the ERP of right and left hand repone poible that did not how a ignificant difference in confidencepecific ERP activity (D certainty ) between effector. While timing and location of the late ERP diociation with choice certainty uggeted a correlation with premotor activity, the ERP difference evidently wa neither locked to the motor repone nor pecific to the movement effector. Electrophyiological correlate of deciion confidence preceded the motor repone, but were neither eential for nor obligatorily linked to it emergence. Moreover, the abence of effector-pecific ERP activity in thi hemipheric contrat made the poiblity implauible that the certainty diociation preceding the motor repone repreented movement execution itelf. Both in Experiment and control for the confounding factor motion coherence (Fig 6b and 9b) made it improbable that the late ERP diociation repreented more frontal contribution to working memory for viual motion oberved in previou moving random-dot experiment 7. Rather one may well ak whether electrophyiological or imaging finding are at leat for comparable dicrimination tak confounded by correlate of ubjective confidence in the perceptual deciion. Earlier in thi dicuion we have etablihed that deciion confidence in Experiment i not traceable before ubject finally commit to a hemifield timulu or pot-cue intruction, repectively, and attention therefore i no longer divided. For invalid cue in Experiment, there wa no certainty-pecific activity preent, a all confidence correlate were confounded by the preented motion coherence (Fig. 5d). In thi line of argument, the ERP diociation with motion coherence following the pot-cue intruction in invalid cue trial may repreent the reactivation and concluding evaluation of timulu-pecific and certainty information after a urpriing turn of event requiring to tart the perceptual deciion again. To hypotheize further, the recall of timulu characteritic in invalid cue may not have been ufficient for detectable confidence correlate to develop. Without elective attention cueing, in Experiment perceptual timulu information entered a fundamentally different tream of NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.

12 NATURE COMMUNICATIONS DOI:.8/ncomm9 cortical proceing right after RDK preentation that did not require later reactivation. While the evaluative procee in perceptual deciion making doubtle culminate in the completion of the deciion, it might be peculated that peri-deciional procee like deciion confidence determine how choen deciion are maintained, protected from competing alternative and enacted 8. Choice certainty in thi model i an apect of metacognition that repreent the invetment of ignificant reource in the proce by which deciion are reached. It motivate ubequent puruit or effort invetment and benefit eventual realization a a high confidence deciion i more likely to be enacted than one fraught with uncertainty 9. We hypotheize that a a conequence choice certainty correlate are perpetuated in preparation of a motor repone. In concluion, our finding reveal electrophyiological correlate of ubjective experience. A ucceion of ERP correlate each reflecting perceptual deciion confidence i independent of objective performance and overt behaviour. Choice certainty evolve in parallel with repreentation of the viual timulu and emerge B m later than repreentation of motion coherence. The certainty-pecific ERP activity topographically reemble repreentation of the enory evidence uggeting a imilar neurophyiological ubtrate. Repreentation of choice certainty over parieto-occipital cortex are not detectable unle or until attention i no longer divided and perit beyond timulu preentation. Thee ditinct correlate are identified during the interval leading to the motor repone, but are independent of movement execution and do not differentiate between motor effector. A deciion-theoretic framework that account for choice certainty may help to improve our undertanding of enoryguided behaviour. Beyond that, of coure, human deciion making extend to abtract deciion about propoition independent of what, if anything, will be done a a conequence. With eparate tream of partial evidence flowing continuouly to the integrator of ubequent deciion, it eem likely that the principle and mechanim of imple perceptual deciion alo upport complex cognitive function and deciion confidence i repreented at thi level of integration. Method Subject. Thirteen ubject were teted in Experiment, data from three ubject were dicarded due to exceive eye blinking or mucle artefact, leaving one lefthanded and nine right-handed participant (three female; mean age ¼.5 year) in the final analyi. Twelve more ubject participated in Experiment, data from two ubject were dicarded ince the highet certainty level (ee below) wa ued too infrequently (o% of trial), leaving ten right-handed participant (five female; mean age ¼.5 year). All ubject had normal or corrected-to-normal viual acuity and reported to be free of neurological or pychiatric impairment. Written informed conent wa obtained from all ubject according to the Declaration of Helinki and the guideline of the local ethic committee of the faculty of medicine of the Univerity of Tübingen, which approved the procedure. white quare (ide length ¼.8 arcmin, lifetime ¼ 5 m, dot denity B6 dot deg, luminance 8 cd m ) on a black background (luminance. cd m ), all moving incoherently, that i, in all poible direction with a reolution of, at a common peed of 6 deg. After the preentation of thi firt pair of RDK (pretimulu; 5 m), a econd pair of RDK, the tet timulu, tarted and wa preented for 5 m,. The propertie of the tet timulu were identical to thoe decribed for the pretimulu except that a certain percentage of the dot element moved coherently in the ame direction (either up, right, down or left). The percentage of coherently moving dot in an individual trial wa choen equally and randomly from four predefined tep (,, or % of all dot). Motion coherence wa alway identical for the two RDK in a given trial, global motion direction could be the ame or different a randomly choen by the computer. After a ubequent econd fixation period (, m), a econd arrow preented for 5 m indicated for which of the two RDK ubject had to report the direction of coherent motion (four-alternative forced choice). Valid cueing a defined by congruent orientation of the precue and the potcue wa applied in 8% of trial. Subject reported their pot-deciion certainty by preing one of four button ued to ignal the perceived motion direction right before. Uniformly, ubject were aked to rate how confident they were in their deciion on a cale of ( being I gueed, I wa ure, and equally paced tep of the continuum in between), ditributing their repone over the available caling. Both repone were given tarting at.5 uing the right hand only and had to be completed within 7 for a trial to be counted, after the econd key pre a new trial would tart automatically. An initial practice run of 5 7 trial familiarized the ubject with the procedure and tabilized dicrimination threhold; thee trial were not ued for further analyi. Each ubject completed about, trial and wa offered everal break. Subject viewed all timuli binocularly from a ditance of 55 cm on a 9 TFT-diplay (native reolution,8, pixel) driven by a Linux computer running the open ource nrec viual timulation, data acquiition and experiment control oftware package ( created by F. Bunje, J. Gukelberger et al.) at a refreh rate of 6 Hz in a dark, quiet room. In Experiment, participant were guided to dicriminate the global direction of one motion timulu preented either right or left of the fixation point. Other than in Experiment, there wa neither an intruction to hift attention nor a econd RDK preented imultaneouly with the tet timulu. Subject would not repond before an arrow pointing left or right indicated which hand they had to repond with, repectively. Both the deciion and the confidence in it were given trial by trial by uing the repone device with the intructed hand. The viual timulu conited of five period, each lating 5 m except for the two fixation period that lated, m (ee Fig. b). Stimulu and repone pecification were otherwie identical to Experiment except for the tet timulu being preented randomly in the right or left viual hemifield, the abence of an attentional cue and the four predefined coherence level being 5, 5, and 7% of all dot. On the bai of the preliminary perceptual threhold of Experiment, the coherence level in the econd experiment were choen differently to better balance the ubject certainty rating for the tatitical analyi. Both repone were given tarting at.5 and had to be completed within 7 for a trial to be counted. After an initial practice run of 5 7 trial, each ubject completed about 8 trial and wa offered at leat two break. EEG wa recorded continuouly during the coure of the experiment. Eye movement recording. During the entire coure of a ingle trial, ubject would fixate the central fixation dot while eye movement were monitored uing a cutom-built video ytem taking the pupil centre a meaure of eye poition. Recording were recorded and tored at a ampling rate of 5 Hz and quality of fixation wa analyed offline. In particular, deviation from the fixation point (eye poition) were examined for the period of tet timulu preentation. All ubject maintained table fixation a indicated by a mean horizontal (h) and vertical (v) eye poition cloe to and mall.d. value: h:.95 ±.5, v-. ±.8 in Experiment and h:. ±., v-. ±. in Experiment. Deign and procedure. To explore electrophyiological correlate of objective and ubjective performance with and without elective attention, we deigned two viual motion perception experiment uing RDK. In Experiment, a patial attention precue-potcue experiment, ubject were intructed to tringently follow an attention cue preceding the timulu. Participant alway had to dicriminate the global direction of one of two motion timuli preented imultaneouly differing in location. They would not repond before a potcue indicated which of the two timuli they actually had to evaluate. Both a deciion and the confidence in it wa given trial by trial, all ubject followed the intruction a illutrated by change of objective performance with attention. EEG wa recorded continuouly during the coure of the experiment. The viual timulu conited of ix period, each lating 5 m except for the econd fixation period, which lated, m (ee Fig. a). After a firt fixation period (central fixation dot, red, diameter arcmin; 5 m) a central arrow (dimenion: x, white, luminance 8 cd m ; 5 m) intructed ubject to covertly hift attention either to the left or right hemifield. Thi attention cue wa followed by two RDK, each of which covered a quare of 9 9 and wa centred right and left, repectively, of the fixation point. Each RDK conited of 75 Electrophyiological recording. EEG wa recorded at 9 calp ite (Fp, Fp, F, F, C, C, P, P, O, O, F7, F8, T7, T8, P7, P8, Fz, Cz, Pz, FC, FC, CP, CP, FC5, FC6, CP5, CP6, TP9 and TP) veru the additional FCz electrode uing an electrode cap equipped with Ag/AgCl electrode (Eaycap, Herrching, Germany). The electro-oculogram (EOG) wa monitored uing an additional electrode placed below the lateral canthu of the right eye. The impedance of the electrode wa kept below ko, EEG and EOG ignal were amplified uing a -channel BrainAmp EEG amplifier (Brainproduct, Munich, Germany). All ignal were continuouly ampled at, Hz and filtered uing a band-pa filter from.5 Hz to 5 Hz. Data analyi. Data analye were performed with cutom-made oftware baed on MATLAB (Mathwork, Natick, MA) and the Fieldtrip toolbox. EEG data were corrected for eye movement artefact uing independent component analyi via CORRMAP within EEGLAB in Experiment and uing Fieldtrip ICA correction in Experiment. All trial then were viually inpected and trial with remaining artefact were excluded from analyi. NATURE COMMUNICATIONS 5:9 DOI:.8/ncomm9 & Macmillan Publiher Limited. All right reerved.