Nature © Macmillan Publishers Ltd 19988letters to nature500 NATURE|VOL 395|1 OCTOBER 1998|www.nature.com7:92 6 0:12 m and 9:68 6 0:19 m, respectively, for the modified blindfolded-walking tasks. The similarity between the results obtained from both types ofwalking task indicates that our modified walking task can also be used toaccurately reflect the observer’s distance judgement.The perceptual matching task. The target viewing conditions were similar tothose used for the walking task. To obtain the observer’s perception of distance,the matching target was placed 908 from the observer. The observer’s task was toview the test target, then turn toward the matching target and instruct theexperimenter to adjust the location of the matching target until it appeared tobe at the same distance from him as the test target.Each observer underwent a practice session before commencing theexperiments. During the proper experiments, the observers were testedunder the same condition two to three times, depending on the particular task.When more than one target distance was tested in an experiment, the order oftesting was counterbalanced across observers.Received 11 May; accepted 16 July 1998.1. Shannon, C. E. & Weaver, W. The Mathematical Theory of Communication (Univ. Illinois Press,Urbana, 1949).2. Gibson, J. J. The Perception of the Visual World (Houghton Mifflin, Boston, 1950).3. Barlow, H. B. in Sensory Communication (ed. Rosenblith, W.) 217–235 (MIT Press, Cambridge,Massachusetts, 1961).4. Attneave, F. Informational aspects of visual perception. Psychol. Rev. 61, 183–193 (1954).5. Sedgwick, H. A. in Human and Machine Vision (eds Rosenthal, A. & Beck, J.) 425–458 (Academic,New York, 1983).6. Thomson, J. A. Is continuous visual monitoring necessary in visually guided locomotion? J. Exp.Psychol. Hum. Percept. Perform. 9, 427–443 (1983).7. Elliot, D. Continuous visual information may be important after all: a failure to replicate Thomson(1983). J. Exp. Psychol. Hum. Percept. Perform. 12, 388–391 (1987).8. Steenuis, R. E. & Goodale, M. A. The effects of time and distance on accuracy of target-directedlocomotion: does an accurate short-term memory for spatial location exist? J. Motor Behav. 20, 399–415 (1988).9. Rieser, J. J., Ashmead, D. H., Talor, C. R. & Youngquist, G. A. Visual perception and the guidance oflocomotion without vision to previously seen targets. Perception 19, 675–689 (1990).10. Loomis, J., DaSilva, J., Fujita, N. & Fukusima, S. Visual space perception and visually directed action.J. Exp. Psychol. 18, 906–921 (1992).11. Loomis, J., DaSilva, J., Philbeck, J. W. & Fukusima, S. Visual perception of location and distance. Curr.Dir. Psychol. Sci. 5, 72–77 (1996).12. Jiang, Y. & Mark, L. S. The effect of gap depth on the perception of whether a gap is crossable. Percept.Psychophys. 56, 691–700 (1994).13. Philbeck, J. W. & Loomis, J. M. Comparison of two indicators of perceived egocentric distance underfull-cue and reduced-cue conditions. J. Exp. Psychol. Hum. Percept. Perform. 23, 72–85 (1997).14. Cutting, J. E. & Vishton, P. M. in Handbook of Perception and Cognition: Perception of Space and MotionVol. 6 (eds Epstein, W. & Rogers, S.) 69–117 (Academic, San Diego, 1995).15. Mark, L. S. Eye-height scaled information about affordances: a study of sitting and stair climbing.J. Exp. Psychol. Hum. Percept. Perform. 13, 360–370 (1987).16. Warren, W. H. & Whang, S. Visual guidance of walking through apertures: body-scaled informationfor affordances. J. Exp. Psychol. Hum. Percept. Perform. 13, 371–383 (1987).17. Sedgwick, H. A. Combining multiple forms of visual information to specify contact relationsin spatiallayout. SPIE 1198, 447–458 (1989).18. He, J. Z. & Nakayama, K. Apparent motion determined by surface layout not by disparity or by 3-dimensional distance. Nature 367, 173–175 (1994).Acknowledgements. This research was supported in part by a Sloan Research Fellowship from the AlfredP. Sloan Foundation (to Z.J.H.) and by a Faculty Research Grant from SCO (to T.L.O.).Correspondence and requests for materials should be addressed to Z.J.H. (e-mail: [email protected]).Shape selectivity in primatelateral intraparietal cortexA. B. Sereno*†& J. H. R. Maunsell*‡* Division of Neuroscience S-603 and‡Howard Hughes Medical Institute,Baylor College of Medicine, Houston, Texas 77030, USA†Center for Molecular and Behavioral Neuroscience, Rutgers University, Newark,New Jersey 07102, USA.........................................................................................................................The extrastriate visual cortex can be divided into functionallydistinct temporal and parietal regions, which have been impli-cated in feature-related (‘what’) and spatial (‘where’) vision,respectively1. Neuropsychological studies of patients withdamage to either the temporal or the parietal regions providesupport for this functional distinction2–4. Given the prevailingmodular theoretical framework and the fact that prefrontal cortexreceives inputs from both temporal and parietal streams5,6, recentstudies have focused on the role of prefrontal cortex in under-standing where and how information about object identity isintegrated with (or remains segregated from) information aboutobject location7–10. Here we show that many neurons in primateposterior parietal cortex (the ‘where’ pathway) show sensoryshape selectivities to simple, two-dimensional geometric shapeswhile the animal performs a simple fixation task. In a delayedmatch-to-sample paradigm, many neuronal units also show sig-nificant differences in delay-period activity, and these differencesdepend on the shape of the sample. These results indicate thatunits in posterior parietal cortex contribute to attending to andremembering shape features in a way that is independent of eyemovements, reaching, or object manipulation. These units showshape selectivity equivalent to any shown in the ventral pathway.Previous studies of the parietal cortex that demonstrated itssensitivity to object shape have tended to focus on tasks involvinghand manipulation of three-dimensional solid objects11–14. Littleattention, however, has been paid to the basic question of simple,two-dimensional shape selectivity in the parietal cortex. Here wetest directly the extent to which units in the lateral intraparietal area(LIP) in posterior parietal cortex respond to differently shaped,two-dimensional