Properties of curvilinear vection

Transcription

1 Perception & Psychophysics / (4), Properties of crvilinear vection XAVIER M. SAUVAN University Hospital, Zrich, Switzerland and CLAUDE BONNET Universite Rene Descartes (Paris VJ, Paris, France Approximately linear relationships were observed between contrast, spatial freqency, temporal freqency, or velocity ofstimlation and perceived velocity of crvilinear vection-that is, a visally indced self-motion in a crved path. Similarly, linear relationships were also fond between the perceived degree of crvatre of crvilinear vection and spatial freqency or velocity ofstimlation. Since the perceived velocity of crvilinear vection varies with contrast, spatial freqency, temporal freqency, and anglar velocity, and the perceived degree ofcrvatre of crvilinear vection varies only with spatial freqency and anglar velocity, peripheral vision is not sfficient for compting accrately the crvilinear component of indced self-motion in a crved path. Concrrently, it was shown that the perceived direction of crvilinear vection is not always nambigosly perceived (Savan & Bonnet, 1989). Conseqently, it is sggested that two different types of visal processing, which involve the peripheral or the central vision, nderlie the processing of crvilinear vection. This experimental work is concerned with the stdy of the properties ofcrvilinear vection. It is the second part ofa more general work, the first part ofwhich is the stdy of the thresholds of linear vections (Savan & Bonnet, 1988, 1989). Vections are indced sensations ofself-motion. It is possible to indce vections by stimlating only a part of the visal field, for example, the central visal field (see Andersen & Branstein, 1985, for rectilinear vection, and Post, 1988, for circlar vection). The perceived direction of vection is always opposite to the direction of the stimlation (Berthoz & Drolez, 1982 Dichgans & Brandt, 1978). Crvilinear vection corresponds to the sensation of taking a bend, and it contains two components, a translational one and a rotational one (Andersen, 1986). It is similar to the actal observer movement in a crved path, sch as moving within a trning vehicle. In the present experimental work, a visal stimlation has been sed to indce crvilinear vection. Vections can also be indced, for example, by visal and vestiblar stimlations in interaction (Dichgans & Brandt, 1978). Indeed, the visal and vestiblar inpts converge in the vestib- The experiments described in this article were carried ot in the Laboratory of Experimental Psychology (UA 316 CNRS & Universiti Rene Descartes). We thank C. Tyler for helpfl comments on earlier versions of the manscript and V. Henn and J. Drolez for their advice. We are gratefl to N. Bonora and C. Bogey for their technical assistance and to G. Loakes for improving or English. X.M.S. particlarly thanks J. Raschecker for his helpfl comments and his kindness dring his stay in the Unit on Neroethology of the NIMH/NIHAC at Poolesville, MD, USA. Correspondence concerning this article shold be addressed to X. Savan, Department of Nerology, University Hospital, Fraenklinikstrasse 26, CH-89l Zrich, Switzerland. lar nclei (Waespe & Henn, 1977, 1978) by a rote involving the ncles of the optic tract and the ncles reticlaris tegmenti pontis with respect to the visal inpts (Howard, 1986), at thalamic level (Bttner & Henn, 1976 Bttner & Lang, 1979) and at cortical level (Bttner & Bettner, 1978 Bttner & Lang, 1979 see also Orban, 1984). Finally, a dominance ofthe visal system can be observed in the case of circlar vection (Bttner & Henn, 1981 Probst, Strabe, & Bles, 1985), which corresponds to an indced rotation abot a vertical axis, or in the case of rectilinear vection (Berthoz & Drolez, 1982 Berthoz, Pavard, & Yong, 1975), which corresponds to an indced translation in a straight line. This reslt shold be related to the existence of nerons in parietal visal area MST in monkey that strongly respond to optic flow stimli (Wrtz & Dffy, 1992). Experimental stdies of locomotion or driving a vehicle in a crved path are sally concerned with real crvilinear movement they are often carried ot within the framework of the comptational analysis of optic flow (e.g., Longet-Higgins & Prazdny, 198 Prazdny, 1981, 1983 Rieger, 1983 see also Andersen, 1986). The aim ofthe present work, therefore, is to stdy with a psychophysical approach the propertiesof crvilinear vection as a fnction of contrast, spatial freqency, temporal freqency, oranglarvelocity ofvisal stimli (Experiments I and 2) and to estimate the temporal characteristics of crvilinear vection (Experiment 3). Crvilinear vection corresponds to locomotion or driving a vehicle in a crved path and is indced by stimlating each eye with a different contrast, spatial freqency, temporal freqency, or anglar velocity (Savan & Bonnet, 1988, 1989). In a more precise way, every factor that introdces enogh 429 Copyright 1993 Psychonomic Society, Inc.

2 43 SAUVAN AND BONNET difference between the apparent velocities oftwo peripheral moving visal patterns, symmetrically placed with respect to the sbject's head, indces crvilinear vection (Savan & Bonnet, 1989). Thresholds of perception of linear vections define a spatiotemporal zone of perception of linear vections, with the thresholds of detection of sinewave gratings motion lying otside of that spatiotemporal area (Savan & Bonnet, 1988, 1989). Crvilinear vection is perceived in the present experimental work by means of peripheral stimlation of low spatial freqency bt small area. Perceived velocity and degree ofcrvatre ofcrvilinear vection vary differently. Moreover, it has been shown that the perceived direction of this vection is not always nambigosly reported (Savan & Bonnet, 1989). It is proposed that the lower and the higher level ambient systems, according to Andersen and Branstein's (1985) theory, shold be involved in the perception of crvilinear vection. GENERAL METHOD Sbjects Seven healthy yong adlts-5 emmetropic females (M.B., N.B., I.G., E.R., and C.T.) and two myopic males (R.P. and X.S.) between the ages of22 and 28-took part in two or three experiments. Apparats The sbjects were seated with their head on a chinrest and were directed to gaze at a fixation point placed before them. Two Tektronix monitors 64 (P3l) were displayed behind two circlar apertres. One apertre sbtended a visal angle of23. The monitors simlated corresponding retinal points. The distance between the sbject's eyes and the screens ofthe monitors was eqal to 25 em. Leibowitz, Rodemer, and Dichgans (1979) have shown that vection is independent of refractive error. Conseqently, the small distance between the monitors and the sbject's eyes shold not have had an effect on the perceived vection. These apertres were made in a half-sphere located in a dark cabin. The mean lminance of the two monitors was 4.15 cd/m'. The centers of the screens of these monitors were placed at an eccentricity of6 on either side ofthe sbjects' sagittal plane. This experimental sitation prodced separate stimlation ofthe two eyes (dichoptic vision) sch that each eye viewed only the monitor in its temporal field. The stimli were vertical sine-wave gratings moving in the nasotemporal direction and generated on the screens ofthe monitors by a "Picasso" CRT Image Generator nder compter control (Z8 microcompter system). The contrast of the gratings is defined as (Lmv,-Lmin)/ (Lmv,+Lmin), in which Lmv, and Lmin are the maximm and minimm lminances of the latter, respectively. The sbjects and the Image Generator nder compter control were located in two different rooms to redce the noise in the experimental room as mch as possible. Procedre The prpose of these experiments was to observe the effect of for variables on the perception ofcrvilinear self-motion indced by sinsoidal drifting gratings. Variables were contrast (C), spatial freqency (SF), temporal freqency (TF), and anglar velocity (V = TF/SF). Five series of asymmetrical visal stimli were sed. The asymmetry D(X) of the stimli was given by the difference between the vale X, of a given variable X on one of the two monitors and the vale X, of the same variable on the other monitor [D(X) = X, - X,]. D(X) was set at a fixed spraliminal vale to indce a crvilinear vection (Savan & Bonnet, 1988, 1989). D(X) was eqal to 15% for contrast,.2 c/deg for spatial freqency, 3 Hz for temporal freqency, and abot 6 deg/sec for anglar velocity. Sch asymmetrical visal stimli are powerfl in indcing crvilinear vection (Savan & Bonnet, 1988, 1989). A single vale ofone ofthe for variables qoted above was presented on each trial of the series, with the exception of the fifth series, in which the variable was a combination of the contrast and the velocity, which varied reciprocally so that the higher the anglar velocity, the lower the contrast, and vice versa. In the contrast condition, contrast varied between 35.4% and 56.4% (Ct) on one monitor and between 2.4% and 41.4% (C,) on the other. In the spatial freqency condition, spatial freqency varied between.23 and.6 c/deg (SF,) on one monitor and between.43 and.8 c/deg (SF,) on the other monitor. In the temporal freqency condition, the temporal freqency varied between 4.6 and 8.14 Hz (TF,) on one monitor and between 1.6 and 5.14 Hz (TF,) on the other. Finally, in the velocity condition, anglar velocity varied between 4.37 and 1.3 deg/sec (V,) on one monitor and between 1.3 and 16.2 deg/sec (V,) on the other. Anglar velocity vales were obtained by sing a freqency matrix (TF/SF), and they were selected from one diagonal of that matrix. In all conditions, the vales on both monitors varied in the same way so that the linear correlation coefficient between those sets ofvales was eqal to 1. Moreover, when one ofthe for variables varied, the vales ofthe three other variables, when they were constant, were close on both monitors to those which defined the optimm of perception of linear vections, that is, 1.2 deg/sec for anglar velocity,.49 c/deg for spatial freqency, 5 Hz for temporal freqency, and 6% for contrast (Savan & Bonnet, 1989). Hlk and Rempt (1983) also fond that anglar velocities from 1 to 15 deg/sec were the most effective in indcing peripheral vertical vection. The difference of velocity between the two sine-wave drifting gratings [D(V) = V,- V,] was constant from one trial to another. This relative velocity was eqal to zero in the contrast condition, 6.25 deg/sec in the temporal freqency condition, and abot 6 deg/sec in the velocity condition. There was a logical exception in the spatial freqency condition, in which the possible effect of the relative velocity variation was netralized by sing relative velocities ranging from 2.5 to 4.65 deg/sec. In for trials, we sed a sbliminal difference of velocity, which did not indce crvilinear vection in the other two trials, we sed a near liminal difference, which indced weak crvilinear vection (Savan & Bonnet, 1988, 1989). It is presmed that any variation of crvilinear vection wold be related to the relative velocity variation in the spatial freqency condition. There were either six or seven trials per series. Indeed, a larger nmber made it difficlt for the sbjects to compare their perceptions of crvilinear vection within a given series. The dration of each trial was 3 sec. The conditions were presented in a different random order to each sbject, and the trials of the series of stimli were also chosen at random. The sbjects were first trained to the sitation before the experiment started. Dring the training, a series of stimli was presented to each sbject to verify if he or she perceived crvilinear vection at each trial. The sbjects reported if they perceived indced selfmotion in a crved path and if they perceived its direction. The perceived direction of indced self-motion in a crved path was the same dring each 3-sec stimls. On the whole, it has been fond that sbjects perceive an indced self-motion in a crved path toward the lowest of the two motions, that is, the lowest apparent velocity (Savan & Bonnet, 1989). At the end of each session and dring the training, the sbjects Were asked ifthey had already experienced indced self-motion when they were seated in an nmoving train and another train was moving in their peripheral visal field. Ifthey answered affirmatively, they were asked whether the indced-self-motion experience in the experiment or dring the training was weaker or stronger than their real-life experience. Frthermore, the sbjects were asked whether this indced-self-motion experience was weaker or stronger than their real-life experience of moving in a vehicle.

3 PROPERTIES OF CURVILINEAR VECTION 431 Finally, "dmmy" series of stimli, in which stimli did not indce self-motion or indced the same perception of vection, were sed dring the training, at the end of several arbitrary chosen sessions, to verify the sbjects' perception of indced self-motion. Statistical Tests Two statistical programs were sed: VAREDI for the analysis of variance in Experiments I and 2 and STAT- ITCF for regression analysis in Experiments I and 2. VAREDI was developed in the Laboratory of Experimental Psychology. EXPERIMENT 1 1 ~ B -" ' 6-4 Qj "C ~ co (f) 2 A The aim of the present experiment was to stdy the variations of the perceived velocity of crvilinear vection as a fnction of contrast, spatial freqency, temporal freqency, and anglar velocity (or contrast and anglar velocity varying reciprocally, in order to test the relative roles of anglar velocity and contrast). Method The five conditions described in the General Method section were presented to 6 trained sbjects (M.B., N.B., R.P., E.R., C.T., and X.S.). A method of direct estimation was sed (Bonnet, 1986) in which the sbjects' task was to estimate the perceived velocity of crvilinear vection with an II-point scale. The sbjects were told that a rating of shold be given if they did not perceive any vection, p to a rating of 1 to be given to the strongest perception of crvilinear vection with respect to its velocity. Dring their training, the sbjects perceived all of the degrees ofcrvilinear vection that they encontered later dring the experiment so that they wold be able to estimate the strongest perception of crvilinear vection in all of the conditions. Reslts and Discssion The independent variables (contrast, spatial freqency, temporal freqency, oranglar velocity) varied in the same way on both monitors (see General Method section). Abscissa vales represent stimli for only one eye in order to make figres intelligible. Perceived velocity of crvilinear vection varied with contrast [F(6,3) = 5.73, P <.1], and this variation was linear [F(I,5) = 6.89, p <.5 r =.76]. The eqation ofthe linear fnction between contrast (C) and perceived velocity of crvilinear vection (VV) was VV = ± C (Figre la). Perceived velocity of crvilinear vection varied with spatial freqency [F(5,25) = 26.22, P <.1], and this variation was linear [F(I,4) = 73.4, P <.1 r = -.974]. The eqation ofthe linear fnction between spatial freqency (SF) and perceived velocity ofcrvilinear vection was VV = ' SF (Figre IB). Perceived velocity of crvilinear vection varied with temporal freqency [F(6,3) = 6, p <.1], and this variation was linear [F(I,5) = 88.78, P <.1 r =.973]. The eqation ofthe linear fnction between temporal freqency (TF) and perceived velocity of crvilinear vection was VV = TF (Figre 2A). Perceived velocity of crvilinear vection varied with anglar velocity [F(6,3) = 18.81, P <.1], and this variation was linear [F(I,5) =4.71,p <.1r=.95]. The eqation of the linear fnction between anglar ve- 1 1 ~ B -" 6 ' - Qj "C Q) 4 (j 2 - (f) Contrast 1%) Spatial freqency lc/degl 5 6 Figre l. (A) Variation of the velocity ofthe perceived crvilinear vection (CLV) as a fnction of the contrast of the stimlation. (8) Variation of the velocity of the perceived crvilinear vection as a fnction of the spatial freqency of the stimlation. Average of 6 sbjects (e) with corresponding sample standard deviation. locity and perceived velocity of crvilinear vection was VV = 8.39' V (Figre 2B). There was a reciprocal variation of the perceived velocity ofcrvilinear vection with anglar velocity and contrast[f(6,3) = 5.1,p <.1]. This reslt seems to indicate an interaction between velocity and contrast. There were two linear correlations: one between perceived velocity ofcrvilinear vection and contrast [F(l,5} = 23.79, P <.1 r = -.91] and another between the same perceived velocity and anglar velocity [F(l,5} = 24.15, p <.1 r =.91]. The eqation ofthe fnction between anglar velocity and perceived velocity of crvilinear vection was VV = 5.51' V , and the eqation between contrast and the same perceived velocity was VV = ' C By comparing these reslts with those obtained in the velocity condition, it can be observed that the slopes of the eqations of regression decreased only from 8.39 to 5.51 (the ratio of the slopes is eqal to 1.52), whereas the slope of the eqation in the condition in which contrast and velocity varied reciprocally is eqal to These facts sggest a preeminence of the velocity of the stimlation over its contrast when the B.8

4 432 SAUVAN AND BONNET 1 ~ 8...J 6?: ' 4 a " Q) 2 n 1 ~...J 8?: 6 ' a 4 A 2 S 4 6 Temporal freqency (Hz) 8 1 Reslts and Discssion As in Experiment 1, abscissa vales represent stimli for one eye. The perceived degree of crvatre of crvilinear vection varied only with spatial freqency [F(5,25) = 7.78, p <.1] or anglar velocity [F(6,3) = 3.71, P <.1]. These variations are shown in Figre 3. This variation was linear for spatial freqency [F(I,4) = , p <.1 r = -.984] and also for anglar velocity [F(I,4) = 17.32,p <.1 r =.88]. Theeqation of the linear fnction between spatial freqency and perceived degree ofcrvatre ofcrvilinear vection (DC) was DC = ' SF + 93 (Figre 3A) and that between anglar velocity and perceived degree ofcrvatre was DC = V +.29 (Figre 3B). The ratio between the slopes ofthe linear fnctions for perceived velocity and perceived degree of crvatre of crvilinear vection with spatial freqency was The ratio was 1.37 when the anglar velocity was the independent variable. The relationship between perceived veloc- 1 A " Q) n Velocity (deg/sec) Figre 2. (A) Variation of the velocity ofthe perceived crvilinear vection as a fnction of the temporal freqency of the stimlation. (B) Variation of the velocity of the perceived crvilinear vection as a fnction of the anglar velocity of the stimlation. Average of 6 sbjects (e) with corresponding sample standard deviation G 9...J ~ :: «i : " Q) n Spatial freqency (c/deg).8 perceived velocity of crvilinear vection is estimated. Contrast has only a secondary effect. Itattenated the sbjects' responses with respect to perceived velocity of crvilinear vection. EXPERIMENT 2 The prpose of this experiment was to observe the effect of the variations ofcontrast, spatial freqency, temporal freqency, and anglar velocity (or contrast and anglar velocity varying reciprocally) on the perceived degree of crvatre of crvilinear vection. Method The conditions and procedre sed in this experiment were exactly the same as those sed in Experiment 1. The task for the sbjects was to estimate, again sing an II-point scale, the perceived degree of crvatre of crvilinear vection. The magnitde of their estimation increased with the degree of crvatre (the higher the 4egree of crvatre, the larger the crved path). Sbjects M.B., N.B., R.P., E.R., C.T., and X.S. took part in Experiment 2. G 9...J Q) : «i 4 : " n '" 2 S' Velocity ldeg/sec) Figre 3. (A) Variation ofthe degree ofcrvatre ofthe perceived crvilinear vection as a fnction ofthe spatial freqency ofthe stimlation. (B) Variation ofthe degree ofcrvatre of the perceived crvilinear vection as a fnction ofthe anglar velocity ofthe stimlation. Average of6 sbjects (e) with corresponding sample standard deviation.

5 PROPERTIES OF CURVILINEAR VECTION 433 ity and degree of crvatre of crvilinear vection has therefore been determined. There was a linear relationship between these two attribtes ofcrvilinear vection when the spatial freqency varied [F(I,4) = ,p <.Olr=.984],theeqation ofthis linear fnction being VV = 1.l3. DC There was also a linear relationship between these variables when the velocity varied [F(I,5) = 11.26, P <.3 r =.832], the eqation of this linear fnction being VV = 1.6 DC Reslts obtained dring Experiments I and 2 show that perceived velocity and degree ofcrvatre ofcrvilinear vection, two attribtes ofthat indced self-motion, varied differently with parameters that define a visal scene, sch as contrast, spatial freqency, temporal freqency, and anglar velocity. Indeed, the perceived velocity of crvilinear vection varied with contrast, spatial freqency, temporal freqency, and anglar velocity, whereas the perceived degree ofcrvilinear vection varied only with spatial freqency and anglar velocity. In the same way, it was observed that perceived degree of crvatre did not vary with spatial freqency, whereas perceived velocity still varied with anglar velocity when apparent depth was present in the visal scene. Two vertical sinewave drifting gratings displayed on the screen of each monitor having different spatial freqencies and velocities indced apparent depth. That observation confirms the different variations ofthe attribtes ofcrvilinear vection as a fnction of the spatiotemporal parameters sed in the present stdy. EXPERIMENT 3 It has been shown that the latency of rectilinear vection (Berthoz et at., 1975) or circlar vection (Brandt, Dichgans, & Koenig, 1973) does not vary with the velocity of the stimlation. The aim of Experiment 3 was to stdy variations of the latency and time of stabilization ofcrvilinear vection as a fnction of contrast, spatial freqency, temporal freqency, and anglar velocity (or contrast and anglar velocity varying reciprocally). Method The same conditions as those sed in Experiments I and 2 were presented to for trained sbjects (M.B., N.B., R.P., and X.S.). The system of response was a joystick connected with a Z8 microcompter. The sbjects' task was to move the joystick when they began to perceive crvilinear vection and then to stop their movement when vection was stabilized. The latency of crvilinear vection and its time of stabilization were measred from the time, that is, the beginning of each trial. The dration of each trial was 22 sec. A preliminary stdy showed that this dration was qite sfficient to perceive steady crvilinear vection. Reslts and Discssion The reslts show that latency and time of stabilization of crvilinear vection did not vary significantly with contrast, spatial freqency, temporal freqency, anglar velocity, or the combination ofthe latter with contrast. Conseqently, it seems that there is no relationship between these variables and latency and time ofstabilization ofcrvilinear vection. Mean latency and mean time of stabilization for the 4 sbjects and the five conditions were 2.4 and 8.37 sec, respectively. Mean latencies for each sbject for all conditions ranged from 1.15 to 5.67 sec mean times of stabilization ranged from 5.64 to sec. The mean latency that Berthoz et al. (1975) measred for rectilinear vection was between I and 2 sec, which is in the same range as the lowest mean latency per sbject measred in the present stdy. GENERAL DISCUSSION Since the sbjects in this stdy of crvilinear vection were in a state ofdichoptic vision, all observed variations of perceived crvilinear vection shold have reqired interhemispheric processing of visal information. It was shown in Experiment 1 that perceived velocity of crvilinear vection decreased with spatial freqency. This reslt is not consistent with that fond for rectilinear vection (Berthoz & Drolez, 1982), which may be related to the fact that the amplitde of postral readjstments varies logarithmically with spatial freqency (Lestienne, Soechting, & Berthoz, 1977). Bt the decrease with spatial freqency is consistent, on the one hand, with the existence of a spatiotemporal zone of perception of linear vections becase crvilinear vection was perceived only if the spatial freqency was below 1 c/deg and, on the other hand, with the vale of the optimm of perception of linear vections for spatial freqency, which is abot.5 c/deg, becase this is a low spatial freqency vale (Savan & Bonnet, 1988, 1989). In the same way as in other indced self-motions in peripheral vision (Berthoz & Drolez, 1982 Dichgans & Brandt, 1978), it was shown in the present stdy that perceived velocity of crvilinear vection increases with anglar velocity. This reslt differs from those of central rectilinear vection stdies that fond a decrease in indced self-motion with increased stimlation velocity (Andersen & Branstein, 1985). The indcing stimls sed by Andersen and Branstein was a radially expanding depth pattern rather than the drifting sine-wave gratings sed in the present stdy. Conseqently, both the optical flow position in the observer's visal field and the optical flow strctre wold playa role in jdging the perceived velocity of vection, with the optical flow defined as the changing strctre of light at an eye cased by the movement ofan organism relative to its environment (see Gibson, 1979). Correspondingly, it has been shown that different classes of optical flow correspond to different classes of self-motions sch as translational and circlar movement (Warren, Mestre, Blackwell, & Morris, 1991). Observed variations of the perceived velocity of crvilinear vection as a fnction of the stimls anglar velocity and spatial freqency show that the experienced velocity of crvilinear vection is dependent on the temporal and spatial characteristics of the stimlation, in the same manner as is circlar vection (de Graaf, Wertheim, Bles, & Kremers, 199). In the present experimental

6 434 SAUVAN AND BONNET work, the sbjects were sddenly exposed to a moving stimlation at the beginning of each trial. This corresponded to a very high visal acceleration. It has been shown that latency of circlar vection has a minimm at 5 deg/sec 2 and increases for slower and faster accelerations ofthe visal stimls (Melcher & Henn, 1981). The latency ofcrvilinear vection, a linear vection with a circlar component, cold also vary as a fnction of the visal stimlation acceleration, althogh this was not investigated in Experiment 3. Or reslts show that attribtes of crvilinear vection vary differently with contrast, spatial freqency, temporal freqency, and anglar velocity. Especially, the perceived velocity of crvilinear vection varies with contrast, spatial freqency, temporal freqency, and anglar velocity, and the perceived degree of crvatre of crvilinear vection varies only with spatial freqency and anglar velocity. Conseqently, nlike the perceived velocity, the perceived degree of crvatre is not always nambigosly estimated, so that the perceived degree of crvatre and the perceived velocity are not always adjsted. That discrepancy and the fact that the perceived direction of crvilinear vection is not always nambigosly perceived (Savan & Bonnet, 1989) indicate that the peripheral visal information is not sfficient to compte the crvilinear component of indced self-motion in a crved path. The central part of the visal field plays a role in perceiving complex self-motion sch as circlar movement (Mestre & Warren, 1989 Warren et al., 1991). Accordingly, two systems appear to control ambient vision: a lower level system that wold reqire peripheral vision and a higher level system that wold work in the central visal field and wold se complex visal information sch as depth ces (Andersen & Branstein, 1985). The primary characteristic of the more primitive system seems to be its sensitivity to low spatial freqencies. Indeed, spatial freqencies below 1 c/deg define the spatiotemporal zone ofperception ofperipheral linear vections so that the optimm ofperception ofperipheral linear vections for spatial freqency is abot.5 c/deg (Savan & Bonnet, 1988, 1989). Moreover, the more primitive ambient system has been described as complementary to the focal system-the former system nderlying spatial orientation and localization, and the latter system nderlying object recognition (Ingle & Sprage, 1975). Correspondingly, the more primitive system may be related to the parietal visal processing stream, and the focal system may be related to the temporal visal processing stream (a recent description ofthese pathways can be fond in Bossaod, Ungerleider, & Desimone, 199). The higher level ambient system of Andersen and Branstein (1985) shold be related to sites of interaction between these two visal processing streams. Several sites of integration of visal inpts relayed over the parietal and temporal visal pathways have been identified (Morel &. Bllier, 199). Some observations indicate that it is important to take into accont not only the visal inpts and processing properties of these systems bt also the pattern oftheir otpt connections (Goodale, Milner, Jakobson, & Carey, 1991). In short, to nderstand the visal control of daily actions sch as locomotion or driving a vehicle, it wold be interesting to stdy variations ofcomplex indced self-motions as a fnction of central and/or peripheral visal stimlations. 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Browman (R.B.W., NASA-Ames Research Ctr., Mail Stop , Moffett Field, CA 9435) "Stereo-motion cooperation and the se of motion disparity in the visal perception of 3D strctre" by V. Cornillea Peres & 1. Drolez (V.C., Lab. de Physiologie Nerosensorielle, 15 re de l'ecolede Medecine, 7527 Paris cedex 6, France) "Organizational factors and the perception of motion in depth" by D.H. Mershon, T.A. Jones, & M.E. Taylor (D.H.M., Dept. of Psychology, North Carolina State Univ., Box 78 I, Raleigh, NC ) "Visal angle as a determinant of perceived inter-object distance" by C.A. Levin & R.N. Haber (C.A.L., 3268 Smmit Ave., Highland Park, IL 635) "Temporal constraints on apparent motion in aditory space" by S. Lakatos (Dept. of Psychology, Jordan Hall, Bldg. 42, Stanford Univ., Stanford, CA 9435) "Limits on the limitations of context conditioned effects in the perception of [b] and [w]" by J.L. Miller & S.c. Wayland (J.L.M., Dept. of Psychology, Northeastern Univ., Boston, MA 2115) "Viewing behavior: Oclar and attentional disengagement" by W.J. Wa & L.B. Stelmach (W.J.W., Commnications Research Ctr., 371 Carling Ave., Ottawa, ONT K2H 8S2, Canada),'Detection ofthree-dimensional srfaces from optic flow: The effects of noise" by G.J. Andersen & A.P. Westefeld (G.J.A., Dept. ofpsychology, Univ. of California, Riverside, CA (426),'Estimating local shape from shading in the presence ofglobal shading" by R.G.F. Erens, A.M.L. Kappers, & J.J. Koenderink (R.G.F.E., Univ. of Utrecht, Princetonplein 5,3584 CC Utrecht, Holland) "What are hman express saccades?" by A. Kingstone & R.M. Klein (A.K., Ctr. for Neroscience, 1633 DaVinci Ct., Univ. of California, Davis, Davis, CA 95616) "Binoclar rivalry of eqilminent targets" by D.H. Westendorf & M. P. Galpo (D.H.W., Dept. of Psychology Univ. of Arkansas Fayetteville, AR ) "Both perceptal and conceptal factors inflence taste-odor and taste-taste interactions" by R.A. Frank, N.J. Van der Klaaw, & H.N.J. Schifferstein (R.A.F., ML #376, Dept. ofpsycho1 ogy, Univ. of Cincinnati, Cininnati, OH ) "Prismatic displacement of vision indces transient changes in the timing of eye-hand coordination" by Y. Rossetti, K. Koga, & T. Mano (Y.R., Vision et Motricite, INSERM Univ., 94-16, Ave. ddoyen Lepine, 695 Bron, France) "The effect of tempo and tone dration on rhythm discrimination" by S. Handel (Dept. of Psychology, Univ. of Tennessee, Knoxville, TN ()9()() "A comparison of thresholds for l/3-octave filtered clicks and noise brsts in infants and adlts" by K.M. Berg (Inst. for Adv. Stdy ofcomm. Processes, 63 Daer Hall, Univ. of Florida, Gainesville, FL 32611) "Tempo sensitivity in aditory seqences: Evidence for a mltiple-look model" by C. Drake & M.-C. Botte (C.D., Lab. de Psy. Exp., 28 re Serpente, 756 Paris, France),'Dration discrimination of empty and filled intervals marked by aditory and visal signals" by S. Grondin (Dept. of Psychology, Larentian Univ., Ramsey Lake Rd., Sdbry, Ontario, Canada P3E 2C6) "Visal inflences on aditory plck and bow jdgments" by H.M. Saldana & L.D. Rosenblm (L.D.R., Dept. of Psychology, Univ. ofcalif., Riverside, Riverside, CA 92521),'Phonatactic knowledge of word bondaries and its se in infant speech perception" by A.D. Friederici & J.M.I. Wessels (A.D.F., Cognitive Science Lab. Berlin, Inst. flir Psy., Freie Univ. Berlin, HabelschwerdterAlle 45, D-looo Berlin 33, Germany)