Journal of Experimental Psychology: Human Perception and Performance

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1 Journal of Experimental Psyhology: Human Pereption and Performane High and Low Roads to Odor Valene? A Choie Response-Time Study Jonas K. Olofsson, Niholas E. Bowman, and Jay A. Gottfried Online First Publiation, July 22, doi: /a CITATION Olofsson, J. K., Bowman, N. E., & Gottfried, J. A. (2013, July 22). High and Low Roads to Odor Valene? A Choie Response-Time Study. Journal of Experimental Psyhology: Human Pereption and Performane. Advane online publiation. doi: /a

2 Journal of Experimental Psyhology: Human Pereption and Performane 2013, Vol. 39, No. 5, Amerian Psyhologial Assoiation /13/$12.00 DOI: /a OBSERVATION High and Low Roads to Odor Valene? A Choie Response-Time Study Jonas K. Olofsson Northwestern University Feinberg Shool of Mediine and Stokholm University Niholas E. Bowman and Jay A. Gottfried Northwestern University Feinberg Shool of Mediine Valene and edibility are two important features of olfatory pereption, but it remains unlear how they are read out from an olfatory input. For a given odor objet (e.g., the smell of rose or garli), does pereptual identifiation of that objet neessarily preede retrieval of information about its valene and edibility, or alternatively, are these proesses independent? In the present study, we studied rapid, binary pereptual deisions regarding odor detetion, objet identity, valene, and edibility for a set of ommon odors. We found that deisions regarding odor-objet identity were faster than deisions regarding odor valene or edibility, but slower than detetion. Mediation analysis revealed that odor valene and edibility deision response times were predited by a model in whih odor-objet identity served as a mediator along the pereptual pathway from detetion to both valene and edibility. Aording to this model, odor valene is determined through both a low road that bypasses odor objets and a high road that utilizes odor-objet information. Edibility evaluations are onstrained to proessing via the high road. The results outline a novel ausal framework that explains how major pereptual features might be rapidly extrated from odors through engagement of odor objets early in the proessing stream. Keywords: olfatory pereption, odor objet oding, valene, emotion Supplemental materials: How are major pereptual features derived from an olfatory input? The present study proposes a novel theoretial framework for olfatory pereption based on response-time (reation time [RT]) measurements and mediation analysis. Jonas K. Olofsson, Department of Neurology, Northwestern University Feinberg Shool of Mediine, Chiago, IL and Department of Psyhology, Stokholm University, Stokholm, Sweden; Niholas E. Bowman and Jay A. Gottfried, Department of Neurology, Northwestern University Feinberg Shool of Mediine. We thank Stefan Wiens and the members of the Gottfried lab for valuable omments, and Connie Choi for exellent assistane. This work was supported with NIH grants to Jay A. Gottfried from the National Institute on Deafness and Other Communiation Disorders (1R01DC010014; K08DC007653), a postdotoral fellowship to Jonas K. Olofsson from the Swedish Researh Counil, and a training grant to Niholas E. Bowman from the National Institutes of Health (T32 AG20506). Jonas K. Olofsson and Niholas E. Bowman ontributed equally to the manusript. Author ontributions: Jonas K. Olofsson and Jay A. Gottfried designed the researh; Jonas K. Olofsson and Niholas E. Bowman performed the researh; Niholas E. Bowman and Jonas K. Olofsson analyzed the data; and Jonas K. Olofsson, Niholas E. Bowman, and Jay A. Gott wrote the artile. Correspondene onerning this artile should be addressed to Jonas K. Olofsson, Department of Psyhology, Stokholm University, Fresati hagväg 9, SE Stokholm, Sweden. jonas.olofsson@psyhology.su.se Among the many possible pereptual attributes of an odor, the features of valene (unpleasant to pleasant) and edibility (low to high) explain a large proportion of the total pereptual variane among odors (Khan et al., 2007; Lawless, 1989; Shiffman, Musante, & Conger, 1978; Stevenson, 2010; Zarzo, 2008). The dominane of these two features reflets the evolutionary legay of the olfatory system, whih is losely affiliated with the limbi system. Even though valene and edibility ratings are often orrelated, they an be dissoiated; perfumes are typially rated as pleasant but not edible, whereas the smell of onion typially shows the opposite pattern (Royet et al., 1999). Although little is yet known about how the brain determines the valene and edibility of an odor, reent findings support an objet-entered approah to olfatory pereption (see Gottfried, 2010; Olofsson, Bowman, Khatibi, & Gottfried, 2012; Wilson & Stevenson, 2006; however, see Yeshurun & Sobel, 2010; Figure 1A). As defined here, odor objets represent those unique qualities or harateristis of an odor (suh as its mintiness or floweriness) that are enoded as memory-based olfatory templates and an guide further proessing. Although objet-entered pereption is a relatively new development in olfatory researh, it is a wellestablished onept in vision researh (Hummel & Biederman, 1992; Logothetis, Pauls, Bulthoff, & Poggio, 1994; Reddy & Kanwisher, 2006; Tanaka, 1993). In our reent work, we showed that pereptual information about odor objets is aessed in advane of information about its valene, and that odor valene does not interfere with odor-objet identifiation (Olofsson et al., 1

3 2 OLOFSSON, BOWMAN, AND GOTTFRIED A Odor objet-entered approah pleasant: yes edible: no B Detetion blok Odor: Present? Yes + No Identifiation blok Odor: XYZ? Yes + No 2012). These findings are in strong agreement with the objetentered approah to olfatory pereption. A key assumption in the objet-entered approah is that odor objets provide ausal links to downstream olfatory proesses (Wilson & Stevenson, 2006). As odor-objet RTs appear to vary systematially aross individuals and odors, they might therefore onstitute a temporal relay to valene and edibility (Olofsson et al., 2012). Suh observations predit that odor-objet identifiation RTs would be a statistial mediator of proessing speed in the pathway from rapid odor detetion to slower valene and edibility deisions. To test this hypothesis, we devised a speeded twoalternative (yes/no) RT experiment in whih partiipants made rapid deisions regarding odor detetion, edibility, valene, and objet identifiation (Figure 1B; some results from one of the experimental onditions in this study were presented as part of a previous study; Olofsson et al., 2012, Experiment 2). Method Valene blok Edibility blok Odor: Pleasant? Yes + No Odor: Edible? Yes + No Figure 1. (A) Illustration of the objet-entered framework and the deision tasks. The objet-entered aount predits that initial formation of a pereptual odor-objet representation (in this example, a rose odor-objet) then ativates systems that determine other pereptual harateristis (valene and edibility). (B) Pereptual deisions were performed with button-press responses. Boxes represent examples of visual ues displayed during the different trials and tasks (XYZ indiates individual odor names that varied aross trials). At the start of eah trial, a 3-s ountdown was followed by the appearane of a red rosshair on the omputer monitor, uing the partiipants to sniff synhronously with the odor pulses. Labels were provided during the prestimulus ountdown. Twenty subjets (12 women; mean age 23.7 years; SD 2.3 years) with no history of igarette smoking, breathing problems, allergies, asthma, smell or taste problems, or neurologial or psyhiatri illness partiipated in the study. Their odor detetion thresholds were in the normal range (min 7.25, max 16.00; M 13.51, SD 2.42; 16 is highest possible sore; Sniffin Stiks, Burghard Instruments; Hummel, Kobal, Gudziol, & Makay-Sim, 2007). Partiipants provided informed onsent to take part in the study, whih was approved by the Northwestern University Institutional Review Board. The stimulus set onsisted of eight familiar, moderately intense odorants that were seleted to systematially vary in valene and edibility: lemon, almond, garli, fish, rose, wood, gasoline, and marker pen (see online supplementary information [SI] for details). The odors were presented using an olfatometer (Plailly, Howard, Gitelman, & Gottfried, 2008). A PC laptop omputer was used for stimulus presentation and response olletion, and for triggering the olfatometer to deliver odors. Partiipants were instruted to exhale during a 3-s ountdown, and to take a sniff at the onset of a following sniff ue (red rosshair). Odor delivery was synhronized with the sniff ue and lasted for 1,000 ms. Breathing belts were used to measure respiratory patterns throughout the experiment (Plailly et al., 2008). During baseline pereptual ratings (i.e., prior to the main RT tasks), partiipants evaluated the following odor harateristis: intensity, pleasantness, familiarity, edibility, and pereptual quality (i.e., how well the odor orresponded to its word label; sales ranged from 10 to 10). Individual odor assessment of eah pereptual attribute was based on the mean of three trials. Eah partiipant performed a total of 120 ratings. The proedure was self-paed, with eah new trial starting 5 s after the previous rating. In four different (randomly ordered) RT tasks, subjets deided as quikly as possible whether odors orresponded to word labels that had been presented just prior to odor onset. The tasks were: detetion (word label: Odor: Present? ), edibility (label: Odor: Edible? ), valene (label: Odor: Pleasant? ), and identifiation (label: Odor: XYZ? where XYZ Lemon, Almond, Garli, Fish, Rose, Wood, Gasoline, or Marker Pen, on separate trials; Figure 1B). Before eah blok, partiipants reeived instrutions in the following format: In the valene task, if you pereive that the odor is pleasant, you press the yes-button, but if it is unpleasant, you press the no-button. For all odor trials, you have to make a quik button-press response based on whether you pereive it to be pleasant or unpleasant. (see SI)

4 HIGH AND LOW ROADS TO ODOR ENCE 3 Odor edibility was defined as whether or not the odor omes from something people normally eat or drink. It does not matter whether you personally like to eat or drink it or not, in an attempt not to onflate edibility with valene (see SI). Eah odor was presented 4 times in eah task, exept for the detetion task, in whih eah odor was presented 2 times, as half the trials were odorless. Only odor trials were onsidered for statistial analyses. Trials were onstruted so that yes and no responses would be balaned. Responses were evaluated from 200 to 5,000 ms postonset of the sniff ue. Odor presentation order was randomized in all tasks. Trials were separated by an 11-s stimulus onset asynhrony to limit sensory habituation. Eah blok lasted about 6 min, with a short break in between bloks. All RT measures were log-transformed to yield normal distributions before further analyses were performed. Kolmogorov Smirnov tests indiated that that our log-transformed RT distributions did not deviate from normality, p(det) 0.915; p(ple) 0.283; p(edi) 0.199; p(id) Hypotheses were tested by means of ANOVAs and regressions. To assess the mediation hypothesis, we used the reommended produt-of-ovariane approah with bootstrapping to empirially estimate variane from 5,000 samples of the indiret effet ab (please note that the bootstrapping method and its expression of produt varianes as onfidene intervals are motivated by the fat that produt varianes are rarely normal; see Preaher & Hayes, 2004). Results and Disussion Ratings, Sniffing, and Behavioral Auray Odors were pereived as being of high intensity (M 5.08, SE 0.56) and familiarity (M 5.01, SE 0.88), and well mathed to their word label (high quality; M 5.21, SE 0.79). Analyses of breathing data showed that sniff magnitudes and onsets were similar aross tasks (ps 0.40; see SI), ensuring that respiratory differenes ould not have aounted for behavioral differenes. In the deision tasks, behavioral auray was high for both detetion (M 95.9%, SD 3.7%) and identity (M 94.4%, SD 3.6%). Binary deisions on the valene RT task orresponded well with preexperimental individual baseline ratings of valene (i.e., whether the valene of an odor was rated as being higher or lower than 0; M 87.0%, SD 7.8%), and the same was true on the edibility RT task when referened to baseline edibility ratings (M 85.3%, SD 11.1%). No response was reorded in 1% of trials, and suh trials were exluded from further analysis. To the extent that odor valene and edibility deisions are subjetive assessments that may flutuate over time, a lak of agreement between preexperimental ratings and later deisions should not be interpreted stritly as error rates. Unless otherwise stated, all responses were inluded in the analyses of RTs (see SI). Response Times: Identifiation Preedes Valene We ompared the mean RT data from the four experimental tasks. There was a signifiant effet of task, F(2.46,44.74) 19.31, p.001, (Figure 2A), with follow-up tests revealing that detetion responses were signifiantly faster than valene responses, p.001, , edibility responses, p.001, , and identity responses, p.002, Identity responses were faster than valene responses, p.039, , and edibility responses, p.001, , and valene and edibility responses approahed signifiane, p.064, The temporal preedene of identity responses before valene and edibility responses is ongruent with previous findings that odor-objet evaluations are faster than odor-valene evaluations for familiar odors (Olofsson et al., 2012). Results from a follow-up analysis showed that exluding error trials did not hange the outomes (see SI). Moreover, when omparing odors that were highly pleasant or unpleasant to odors that were rated as more neutral, or when omparing odors of high or low edibility to odors rated as more ambiguous, the main outomes were unhanged (Figure 2B; see SI for details). The order of task ompletion were thus unlikely to be aounted for by speed auray trade-offs, or by odors that were ambiguous or inonsistently ategorized with regards to valene or edibility. A Causal Path From Identifiation to Valene Given the temporal preedene of identity responses before valene and edibility responses (f. Figure 2) and our previous results of a proessing advantage for objet-based deisions (Olofsson et al., 2012), it is reasonable to hypothesize that the valene and edibility of an odor is ausally determined after extrating information about its objet identity (Wilson & Stevenson, 2006). Whether odor-objet identity represents a ausal step linking stimulus input to valene (or edibility) determination was modeled using mediation analysis (Figure 3), whih is helpful for haraterizing the temporal, sequential unfolding of psyhologial proesses (Collins, Graham, & Flaherty, 1998). In this model, we used all eight odors for all 20 subjets as data points, beause even if a given odor objet might be ativated at different times for different individuals, the temporal assoiations outlined above should remain (see Figure 3B). However, beause we were only interested in within-subjet variations, we ontrolled for effets related to subjet (Bland & Altman, 1995; Collins et al., 1998). We onstruted a mediation model of the RT data that inluded a diret proessing route from detetion (the preditor) to valene (the outome), and an indiret route linking detetion and valene by way of identifiation (the mediator). By determining the signifiane of the diret and indiret routes, the model tested whether the relationships between our key variables would onform to either parallel routes (no mediation), a serial (mediated) route, or dual proessing routes (both mediated and unmediated; Figure 3B, 3C). Either of the two latter possibilities would onstitute evidene of identifiation as a mediator (Zhao, Lynh, & Chen, 2010) of valene, and help validate an objet-based aount of human olfatory pereption. The results showed a signifiant effet of the indiret route (path ab), 0.197, 99% CI [0.0890, ], onsistent with mediation (note that this produt variane is better expressed in CI rather than as a p value beause it is typially not normally distributed; see Preaher & Hayes, 2004). There was also an effet of the diret route (path ) from detetion to valene RTs, 0.284, p.001. This pattern of findings thus onforms to a dual route (Figure 3D, left) by whih odor valene an be aessed by both diret and indiret routes. The proportion explained variane (R 2 ) of the model was 41.0%. In a follow-up analysis, the rated absolute deviation from the valene midpoint

5 4 OLOFSSON, BOWMAN, AND GOTTFRIED A 7.5 Response times (log) Response times (log) B Detetion 1 p = Detetion Identity Valene Edibility Valene Detetion p = Detetion p = Edibility Easy to Hard to Easy to Hard to lassify lassify lassify lassify Valene Edibility Edibility 1100 Valene 1000 Identity Identity Identity 900 Identity 800 Detetion Response times (ms) Response times (ms) Figure 2. (A) Identifiation RTs preede valene and edibility RTs. (B) Mean RTs ( SE) assoiated with the four different task RTs were alulated separately for odors that were divided into easy and hard to lassify based on how muh they deviated from the midpoint of the valene and edibility rating sales. Four odors were plaed in eah ategory, based on the preexperimental ratings of eah partiipant. The staked graphs illustrate that the temporal order by whih the RT tasks were ompleted did not differ for easy versus hard odors. (determined for eah individual and odor) was used as a ovariate. Although this variable explained a signifiant portion of the variane in valene RT, p.002, indiating that an effet was present at the valene response stage, it is important to note that it did not diminish the mediation effet of the indiret route, 0.179, 99% CI [0.0848, ], indiating that the original model was robust. Applying the same approah to edibility responses (the outome in the mediation model), we also found evidene for me-

6 HIGH AND LOW ROADS TO ODOR ENCE 5 A B -mediating -non-mediating Preditor a Mediator b Outome O1 O2 O3 O1 O2 O3 C Parallel route Serial route Dual route a b a b a b D diation, suh that the indiret path ab was signifiant, 0.233, 99% CI [0.1171, ]. However, there was no evidene of a diret path from detetion to edibility responses, 0.045, p.461. The proportion explained variane (R 2 ) of the model was 34.6%. The rated absolute deviation from the edibility midpoint (determined for eah individual and odor) was used as a ovariate in a follow-up analysis. Although this variable explained a signifiant portion of the variane in edibility responses, p.01, indiating an effet present at the response stage, it did not influene the mediation effet of the indiret route, 0.233, 99% CI [0.1189, ]. This pattern onforms to the serial route (Figure 3D, right), whereby the extration of odor-objet information mediates odor edibility with no diret pathway. Other analyses inluded odor intensity and odor familiarity as ovariates in the mediation model, but these ovariates had no signifiant influene (ps 0.50) and did not affet the results. In sum, the results from the mediation analyses of RTs show that objet identifiation mediates valene and edibility upon deteting an odor. Although muh researh on the human olfatory system fouses on outlining its spatial harateristis by means of funtional neuroimaging, in this study we fous instead on the time domain, using RTs to outline the olfatory pereptual asade. Previously, the notion of high and low roads has been invoked to desribe information flow toward the amygdala via ortial and subortial iruits to generate affetive responses (LeDoux, 2000; Morris, Öhman, & a ab * * b ENCE a ab * b EDIBILITY Figure 3. (A) Results from the mediation analyses. This shemati depits a anonial mediation model that inludes both diret () and indiret effets (a b); speifially, is the assoiation between preditor and outome that remains after the indiret effet ab is inluded in the regression (B). Hypothetial omparative RT profiles for three odors (O1 O3) in a ase where identifiation mediates valene (left box) and in a ase where it does not (right box). These profiles illustrate a systemati relationship between identifiation () RTs and valene () RTs only if mediates aess to valene information. Here, the RTs are referened to odor detetion (), whih is onsidered the preditor in the model (C). Possible outomes of the mediation analysis, with thik arrows indiating signifiant relationships, inluding models in whih the link from to is diret and independent of (parallel routes to and, no mediation), indiret and reliant on (serial route), or a ombination of diret and indiret effets (dual route). Separate analyses were onduted with valene replaed by edibility (D). Results indiate that valene is proessed through dual routes (both ab and are signifiant), whereas edibility is proessed through a serial route (only ab is signifiant). p.001 for diret effets and 99% CI for indiret effets. Dolan, 1999). Based on our findings, we propose, analogously, that odor valene is determined in part by input from a high road, whih involves objet reognition of familiar odors. The odor objets are thus not defined by their valene, but rather define valene, that is, odor objets ativate emotional responses downstream. The pereptual aspet of the odor objet is likely represented in the piriform ortex; this region has extensive projetions to and from other assoiative orties (Carmihael, Clugnet, & Prie, 1994; Johnson, Illig, Behan, & Haberly, 2000), enabling pereptual learning and odor quality oding, whih omprise essential features of objet pereption in the olfatory domain (Gottfried, Winston, & Dolan, 2006; Haberly, 2001; Howard, Plailly, Grueshow, Haynes, & Gottfried, 2009; Li, Luxenberg, Parrish, & Gottfried, 2006). Semanti attributes of the odor objet might be represented in the anterior temporal lobes (Olofsson, Rogalski, Harrison, Mesulam, & Gottfried, 2013; Patterson, Nestor, & Rogers, 2007), and the orbitofrontal ortex and amygdala might represent emotional intensity and olfatory reward value (Gottfried & Dolan, 2004; Gottfried, O Doherty, & Dolan, 2003; Zald & Pardo, 1997). In the ontext of this framework, it seems plausible that for familiar odors, the high road involves ausal engagement of odor objets in piriform ortex and heteromodal regions, but the low road does not. In ontrast to valene, edibility might only be aessed indiretly through the high road, and we speulate that there may thus be no suh thing as a general pereptual lass of intrinsi food odors that would inlude smells as diverse as fish and

7 6 OLOFSSON, BOWMAN, AND GOTTFRIED lemon. Suh judgments might always require pereptual analysis provided by the high road. Our mediation analysis was informed by modern approahes that have largely replaed the traditional ausal steps approah (Baron & Kenny, 1986) beause of its oneptual and empirial shortomings (Hayes, 2009; MaKinnon, Lokwood, Hoffman, West, & Sheets, 2002). We note that statistial mediation analysis does not require establishing a temporal sequene of response variables, and indeed, mediation analysis is often used in surveybased psyhologial researh without onsideration of RTs, but mediation models should only be used when they are theoretially justified. In the present study, beause only objet identifiation was a priori hypothesized as a mediator, we were onservative in elaborating on more omplex mediation models. However, an exploratory analysis indiated that, seond to objet identifiation, odor valene might onstitute a seondary mediator to determine edibility RT responses within the high road (see SI for details). Future studies may investigate the role of suh omplex mediation pathways, as well as differenes related to prior olfatory exposure and learning (Stevenson & Wilson, 2007), and the role of retronasal and orthonasal stimulation of food odors, within the general framework of high and low roads in olfatory objet pereption. Our study shows that probing the temporal harateristis of the pereptual asade might yield unique information about the proessing pathways of the human olfatory system. Referenes Baron, R. M., & Kenny, D. A. (1986). The moderator mediator variable distintion in soial psyhologial researh - oneptual, strategi, and statistial onsiderations. Journal of Personality and Soial Psyhology, 51, Bland, J. M., & Altman, D. G. (1995). Calulating orrelation oeffiients with repeated observations: Pt. 1 Correlation within subjets. British Medial Journal, 310, 446. doi: /bmj Carmihael, S. T., Clugnet, M. C., & Prie, J. L. (1994). Central olfatory onnetions in the maaque monkey. Journal of Comparative Neurology, 346, doi: /ne Collins, L. M., Graham, J. W., & Flaherty, B. P. (1998). An alternative framework for defining mediation. Multivariate Behavioral Researh, 33, doi: /s mbr3302_5 Gottfried, J. A. (2010). Central mehanisms of odour objet pereption. Nature Reviews Neurosiene, 11, doi: /nrn2883 Gottfried, J. A., & Dolan, R. J. (2004). Human orbitofrontal ortex mediates extintion learning while aessing onditioned representations of value. Nature Neurosiene, 7, doi: /nn1314 Gottfried, J. A., O Doherty, J., & Dolan, R. J. (2003). Enoding preditive reward value in human amygdala and orbitofrontal ortex. Siene, 301, doi: /siene Gottfried, J. A., Winston, J. S., & Dolan, R. J. (2006). Dissoiable odes of odor quality and odorant struture in human piriform ortex. Neuron, 49, doi: /j.neuron Haberly, L. B. (2001). Parallel-distributed proessing in olfatory ortex: New insights from morphologial and physiologial analysis of neuronal iruitry. Chemial Senses, 26, doi: /hemse/ Hayes, A. (2009). Beyond Baron and Kenny: Mediation analysis in the new millennium. Communiation Monographs, 76, doi: / Howard, J. D., Plailly, J., Grueshow, M., Haynes, J. D., & Gottfried, J. A. (2009). Odor quality oding and ategorization in human posterior piriform ortex. Nature Neurosiene, 12, doi: /nn.2324 Hummel, J. E., & Biederman, I. (1992). Dynami binding in a neural network for shape-reognition. Psyhologial Review, 99, doi: / x Hummel, T., Kobal, G., Gudziol, H., & Makay-Sim, A. (2007). Normative data for the Sniffin Stiks inluding tests of odor identifiation, odor disrimination, and olfatory thresholds: An upgrade based on a group of more than 3,000 subjets. European Arhives of Oto-Rhino- Laryngology, 264, doi: /s Johnson, D. M. G., Illig, K. R., Behan, M., & Haberly, L. B. (2000). New features of onnetivity in piriform ortex visualized by intraellular injetion of pyramidal ells suggest that primary olfatory ortex funtions like assoiation ortex in other sensory systems. Journal of Neurosiene, 20, Khan, R. M., Luk, C. H., Flinker, A., Aggarwal, A., Lapid, H., Haddad, R., & Sobel, N. (2007). Prediting odor pleasantness from odorant struture: Pleasantness as a refletion of the physial world. The Journal of Neurosiene, 27, doi: /jneurosci Lawless, H. T. (1989). Exploration of fragrane ategories and ambiguous odors using multidimensional saling and luster analysis. Chemial Senses, 14, doi: /hemse/ LeDoux, J. E. (2000). Emotion iruits in the brain. Annual Review of Neurosiene, 23, doi: /annurev.neuro Li, W., Luxenberg, E., Parrish, T., & Gottfried, J. A. (2006). Learning to smell the roses: Experiene-dependent neural plastiity in human piriform and orbitofrontal orties. Neuron, 52, doi: /j.neuron Logothetis, N. K., Pauls, J., Bulthoff, H. H., & Poggio, T. (1994). Viewdependent objet reognition by monkeys. Current Biology, 4, doi: /s (00) MaKinnon, D. P., Lokwood, C. M., Hoffman, J. M., West, S. G., & Sheets, V. (2002). A omparison of methods to test mediation and other intervening variable effets. Psyhologial Methods, 7, doi: / X Morris, J. S., Öhman, A., & Dolan, R. J. (1999). A subortial pathway to the right amygdala mediating unseen fear. Proeedings of the National Aademy of Sienes of the United States of Ameria, 96, doi: /pnas Olofsson, J. K., Bowman, N. E., Khatibi, K., & Gottfried, J. A. (2012). A time-based aount of odor objets and valenes. Psyhologial Siene, 23, doi: / Olofsson, J. K., Rogalski, E., Harrison, T., Mesulam, M., & Gottfried, J. A. (2013). A ortial pathway to olfatory naming. Evidene from primary progressive aphasia. Brain: A Journal of Neurology, 136, Patterson, K., Nestor, P. J., & Rogers, T. T. (2007). Where do you know what you know? The representation of semanti knowledge in the human brain. Nature Reviews Neurosiene, 8, doi: /nrn2277 Plailly, J., Howard, J. D., Gitelman, D. R., & Gottfried, J. A. (2008). Attention to odor modulates thalamoortial onnetivity in the human brain. The Journal of Neurosiene, 28, doi: / JNEUROSCI Preaher, K. J., & Hayes, A. F. (2004). SPSS and SAS proedures for estimating indiret effets in simple mediation models. Behavior Researh Methods, Instruments & Computers, 36, doi: /bf Reddy, L., & Kanwisher, N. (2006). Coding of visual objets in the ventral stream. Current Opinion in Neurobiology, 16, doi: /j.onb Royet, J. P., Koenig, O., Gregoire, M. C., Cinotti, L., Lavenne, F., Le Bars, D.,... Froment, J. C. (1999). Funtional anatomy of pereptual and semanti proessing for odors. Journal of Cognitive Neurosiene, 11, doi: / Shiffman, S. S., Musante, G., & Conger, J. (1978). Appliation of multidimensional-saling to ratings of foods for obese and normal weight

8 HIGH AND LOW ROADS TO ODOR ENCE 7 individuals. Physiology & Behavior, 21, doi: / (78) Stevenson, R. J. (2010). An initial evaluation of the funtions of human olfation. Chemial Senses, 35, doi: /hemse/bjp083 Stevenson, R. J., & Wilson, D. A. (2007). Odour pereption: An objetreognition approah. Pereption, 36, doi: /p5563 Tanaka, K. (1993). Neuronal mehanisms of objet reognition. Siene, 262, doi: /siene Wilson, D. A., & Stevenson, R. J. (2006). Learning to smell: Olfatory pereption from neurobiology to behavior. Baltimore, MD: Johns Hopkins University Press. Yeshurun, Y., & Sobel, N. (2010). An odor is not worth a thousand words: from multidimensional odors to unidimensional odor objets. Annual Review of Psyhology, 61, Zald, D. H., & Pardo, J. V. (1997). Emotion, olfation, and the human amygdala: Amygdala ativation during aversive olfatory stimulation. Proeedings of the National Aademy of Sienes of the United States of Ameria, 94, doi: /pnas Zarzo, M. (2008). Psyhologi dimensions in the pereption of everyday odors: Pleasantness and edibility. Journal of Sensory Studies, 23, doi: /j x x Zhao, X., Lynh, J. G., Jr., & Chen, Q. (2010). Reonsidering Baron and Kenny: Myths and truths about mediation analysis. Journal of Consumer Researh, 37, doi: / Reeived Deember 20, 2012 Revision reeived Marh 20, 2013 Aepted April 12, 2013