The effects of number of stimuli and prior exposure on performance of concurrent visual discriminations during suppression of inferotemporal cortex with cold

Subdivisions of inferior temporal cortex in squirrel monkeys make dissociable contributions to visual learning and memory

Inferior temporal cortex of squirrel monkeys consists of caudal (ITC), intermediate (ITI), and rostral (ITR) subdivisions, possibly homologous to TEO, posterior TE, and anterior TE of macaque monkeys. The present study compared visual learning in squirrel monkeys with ablations of ITC; ITI and ITR (group ITRd); or ITI, ITR, and more ventral cortex, including perirhinal cortex (group ITR+), with visual learning in unoperated controls. The ITC monkeys had significant impairments on pattern discriminations and milder deficits on delayed non-matching to sample (DNMS) of objects. The ITRd monkeys had deficits on some pattern discriminations but not on DNMS. The ITRd monkeys were significantly impaired on DNMS and some pattern discriminations. These results are similar to those found in macaques and support the proposed homologies.

Perception, learning and identification studied with reversible suppression of cortical visual areas in monkeys

We use cold to reversibly suppress cortical areas involved in visual perception, learning and retrieval and we found a localization of functions essential for performance of delayed match-to-sample (DMS) in anterior ventral temporal cortex, we call ventral TE (TEv). We also found a visual input for this area that is separate from the one going to the heart of inferotemporal cortex and suppressing this input also impairs performance of DMS. Suppressing the dorsal half of TE (TEd) disrupts retrieval of some, but not all complex images, and different images are disrupted in different animals. This variability within and between animals is extreme, with perfect performance on some complex images and below chance on others. We suggested that TEd represents some, but not all elements of the images. In attempting to discover what those elements might be, we found that TEd suppression disrupts the perception of small figures, but not the larger figures that they compose. We also found that it impaired the discrimination and matching of colors, without impairing the ability to detect and differentiate hues. We proposed that TEd represents the details and colors of things, but not global figures. Also, complex objects do not have a representation in one area, rather its representation involves the entire visual system, including TE with different elements of the image represented in different parts.

Local and global perception examined by reversible suppression of temporal cortex with cold

We placed cryodes over both sides of the dorsal inferotemporal cortex (TEd) in three monkeys in order to suppress its functions during perception of compound visual images. We used three pairs of images in a concurrent visual discrimination: 1. Congruent pair, a large T made of small Ts and a large 7 made of small 7s with response to the large 7 rewarded. 2. Incongruent pair, a T made of small 7s and a 7 made of small Ts with response to the large 7 rewarded. 3. Random pair, a scattering of small Ts in one stimulus and small 7s in the other with response to the small 7 rewarded. If TEd processes the global but not the local elements of a visual figure, animals with TEd suppressed should see only the local figures and they would fail only on the incongruent stimulus. Alternatively, if TEd processed the local, but not the global elements, they should fail only on the scattered small figures where there was no global element as a cue. Finally, if TEd suppression impairs discrimination of forms, they should be impaired on all the figures because they were the same form, but different size. We found that during TEd suppression, the animals failed on the scattered small elements, but not on the global figures formed of the small elements.

Retrieval of color and form during suppression of temporal cortex with cold

Five cryodes were implanted on each side over the dorsal aspect of inferotemporal cortex (TEd) of three monkeys. They were trained on a form discrimination and three color discriminations. Suppression of TEd with cold disrupted retrieval of the color, but not the form discriminations. The animals could find the colors in a background of shifting values of gray, indicating that the suppression did not reduce their color perception to gray. They initially had great difficulty matching red to red and green to green, although that recovered with experience. The animals tended to respond to one or the other of the colors, indicating that they could perceive and discriminate them, but, either lost information about the correct stimulus, or something from past experience was interfering with performance. We suggested that cooling TEd suppresses new and recent learning of color discriminations, but it does not suppress some previous experience that intrudes upon performance of new tasks. TEd might contain episodic information about colors necessary for performance of the immediate task.