Exp Brain Res (1992) 88:292-302 Experimental BrainResearch © Springer-Verlag 1992 Effects of inferotemporal cortex lesions on form-from-motion discrimination in monkeys Kenneth H. Britten 1, William T. Newsome I, and Richard C. Saunders 2 l Department of Neurobiotogy, Stanford University School of Medicine, Stanford, CA 94305, USA 2 Clinical Brain Disorders Branch, NIMH Neuroscienccs Center, St. Elizabeth's Hospital, Washington, DC 20032, USA Received June 6, 1991 / Accepted September 23, 1991 Summary. The inferotemporal cortex of primates plays a prominent role in the learning and retention of visual form discriminations. In this experiment we investigated the role of inferotemporal (IT) cortex in the discrimina- tion of two-dimensional forms defined by motion cues. Six monkeys were trained to a criterion level of perfor- mance on two form-from-motion problems. Three of these animals received complete bilateral lesions of IT cortex, while the other three served as unoperated con- trols. All animals were then retrained to criterion to evaluate the effects of IT lesions on the retention of form-from-motion learning. Compared with the control group, the lesion group was significantly impaired on both problems. Following retention testing, we trained both groups of monkeys on two new form-from-motion problems to investigate the effects of IT lesions on ac- quisition rates for new learning. The lesion group per- formed well on the new problems; the learning rates of the operated and control groups were not significantly different. When forms were defined by luminance cues, monkeys with IT lesions, like those in previous studies, were impaired both for retention and for acquisition. These findings indicate that the anterograde effects of IT lesions on learning new form discriminations are less severe for forms defined by motion cues than for forms defined by luminance cues. However, the retrograde ef- fects of IT lesions on retention are severe for forms defined by either cue. Key words: Extrastriate visual cortex - Inferotemporal cortex - Motion processing - Cortical pathways - Lesion effects - Structure-from-motion Introduction Behavioral and anatomical evidence indicates that extra- striate visual cortex of primates consists of at least 2 major pathways with distinct functional roles (Unger- Offprint requests to: K.H. Britten leider and Mishkin 1982). A ventral pathway connecting the striate and posterior extrastriate visual areas with inferior temporal (IT) cortex is involved in the identifica- tion of patterns and is often referred to as the "form pathway". The second pathway" courses more dorsally and connects striate and extrastriate areas with inferior parietal cortex. This pathway, which is often referred to as the "spatial pathway", contributes to the visual loc- alization of objects and is involved in the control of visual attention as well. Removal of IT cortex in mon- keys results in striking deficits on form and object recog- nition tasks, while the ability to localize objects in space appears unaffected. The opposite pattern of effects oc- curs after removal of the posterior parietal cortex (Mish- kin et al. 1982; Mishkin and Ungerleider 1982; Pohl 1973), although the spatial localization deficits that fol- low parietal lesions may result in part from an attentional impairment (Lawler and Cowey 1987). These results are consistent with clinical observations of human patients with restricted cortical damage. Temporal lobe lesions can cause various agnosias involving identification or recognition of visual stimuli (Damasio et al. 1982; Kimu- ra 1963; Meadows 1974), while parietal lesions often result in mislocalization of visual stimuli (Cole et al. 1962; Holmes 1918; Ratcliff and Davies-Jones 1972) as well as impaired spatial attention (Battersby et al. I956; Brain 1941 ; Heilman et al. 1970; Heilman and Valenstein 1979). Motion is a fundamental visual dimension that is used both for the perception of form and for the analysis of spatial relations between objects. Psychophysical studies have provided ample evidence that relative motion cues are important for segregating and identifying two-dimen- sional forms and for identifying the shape of three- dimensional surfaces (Nakayama and Loomis 1974; Wallach and O'Connell 1953). In addition, motion in- formation is of critical importance for establishing an accurate representation of the spatial relationships be- tween moving objects and for orienting visual attention. Thus one might expect motion information to be promi- nently represented at the single neuron level in both the