Recently, we identified, using fMRI, three bilateral regions in the ventral temporal cortex that responded preferentially to faces, houses, and chairs [Ishai, A., Ungerleider, L. G., Martin, A., Schouten, J. L., & Haxby, J. Y. (1999). Distributed representation of objects in the human ventral visual pathway. Proceedings of the National Academy of Sciences, U.S.A., 96 , 9379-9384]. Here, we report differential patterns of activation, similar to those seen in the ventral temporal cortex, in bilateral regions of the ventral occipital cortex. We also found category-related responses in the dorsal occipital cortex and in the superior temporal sulcus. Moreover, rather than activating discrete, segregated areas, each category was associated with its own differential pattern of response across a broad expanse of cortex. The distributed patterns of response were similar across tasks (passive viewing, delayed matching) and presentation formats (photographs, line drawings). We propose that the representation of objects in the ventral visual pathway, including both occipital and temporal regions, is not restricted to small, highly selective patches of cortex but, instead, is a distributed representation of information about object form. Within this distributed system, the representation of faces appears to be less extensive as compared to the representations of nonface objects.

Visual imagery and perception share several functional properties and apparently share common underlying brain structures. A main approach to the scientific study of visual imagery is exploring the effects of mental imagery on perceptual processes. Previous studies have shown that visual imagery interferes with perception (Perky effect). Recently we have shown a direct facilitatory effect of visual imagery on visual perception. In an attempt to differentiate the conditions under which visual imagery interferes or facilitates visual perception, we designed new experimental paradigms, using detection tasks of a Gabor target. We found that imagery-induced interference and facilitation are memorydependent: Visual recall of common objects from long-term memory can interfere with perception, while on short-term memory tasks facilitation can be obtained. These results support the distinction between low-level and structural representations in visual memory.

Visual imagery is the invention or recreation of a perceptual experience in the absence of retinal input.The degree to which the same neural representations are involved in both visual imagery and visual perception is unclear. Previous studies have shown that visual imagery interferes with perception (Perky effect). We report here psychophysical data showing a direct facilitatory effect of visual imagery on visual perception. Using a lateral masking detection paradigm of a Gabor target, flanked by peripheral Gabor masks, observers performed imagery tasks that were preceded by perceptual tasks. We found that both perceived and imaginary flanking masks can reduce contrast detection threshold. At short target-to-mask distances imagery induced a threshold reduction of 50% as compared with perception, while at long target-to-mask distances imagery and perception had similar facilitatory effect. The imagery-induced facilitation was specific to the orientation of the stimulus, as well as to the eye used in the task. These data indicate the existence of a stimulus-specific short-term memory system that stores the sensory trace and enables reactivation of quasi-pictorial representations by topdown processes. We suggest that stimulus parameters dominate the imagery-induced facilitation at short target-to-mask distances, yet the topdown component contributes to the effect at long target-to-mask distances.