Perceptual Learning of Simple Stimuli Modifies Stimulus Representations in Posterior Inferior Temporal Cortex

Abstract

Practicing simple visual detection and discrimination tasks improves performance, a signature of adult brain plasticity. The neural mechanisms that underlie these changes in performance are still unclear. Previously, we reported that practice in discriminating the orientation of noisy gratings (coarse orientation discrimination) increased the ability of single neurons in the early visual area V4 to discriminate the trained stimuli. Here, we ask whether practice in this task also changes the stimulus tuning properties of later visual cortical areas, despite the use of simple grating stimuli. To identify candidate areas, we used fMRI to map activations to noisy gratings in trained rhesus monkeys, revealing a region in the posterior inferior temporal (PIT) cortex. Subsequent single unit recordings in PIT showed that the degree of orientation selectivity was similar to that of area V4 and that the PIT neurons discriminated the trained orientations better than the untrained orientations. Unlike in previous single unit studies of perceptual learning in early visual cortex, more PIT neurons preferred trained compared with untrained orientations. The effects of training on the responses to the grating stimuli were also present when the animals were performing a difficult orthogonal task in which the grating stimuli were task-irrelevant, suggesting that the training effect does not need attention to be expressed. The PIT neurons could support orientation discrimination at low signal-to-noise levels. These findings suggest that extensive practice in discriminating simple grating stimuli not only affects early visual cortex but also changes the stimulus tuning of a late visual cortical area.

Perceptual learning of fine contrast discrimination changes neuronal tuning and population coding in macaque V4

“…Switching attention between trained and untrained locations did not trigger the training-induced shift in PNE, indicating that learning-induced changes arose from long-lasting enhancements in neurons’ ability to represent stimulus contrast differences, rather than to attention-evoked or other task-evoked modulations of firing rates (see also Supplementary note 10 ). This is in line with data from posterior inferior temporal area, which is hierarchically close to area V4 12 . Interestingly, the results are different from similar studies in area V1 41 , where neural correlates of perceptual learning were task-dependent, and thus possibly related to selective attention 7 .…”

“…refs. 9 – 12 ). Only one study has analysed striate cortex (V1) activity from multiple chronically implanted electrodes during learning.…”

Top-down modulation of sensory cortex gates perceptual learning

“…For example, Gilbert and colleagues found that while perceptual training on an embedded contour detection task has little effect on basic response properties of monkey V1 neurons, it has a pronounced effect on how V1 neurons are modulated by stimulus context (6,56,71). This finding stands in contrast to those described above from V4 (57,70) and primary ACx (9)(10)(11)(12), where it was found that training modified stimulus-encoding properties. These apparent dissimilarities may reflect differences among functional networks, behavioral tasks, or species.…”

“…These studies report that trained animals display altered auditory cortical responses, such as tonotopic reorganization (9,12) and enhanced AM processing (10,11). Similarly, Adab and colleagues recorded from V4 and posterior inferior temporal cortex neurons of awake monkeys during training on an orientation discrimination task (57,70). The authors found that training enhanced the responses to the orientation gratings, and the enhancements were present both during task performance and during passive fixation.…”

Crossmodal Association of Visual and Haptic Material Properties of Objects in the Monkey Ventral Visual Cortex

“…It is unlikely that this reflects visual experience alone. Moreover, some studies have shown that fMRI activity patterns are immune to visual training and familiarization in adult monkeys [27,28], although the activity magnitudes may change [29]. Taken together, representational changes in the PIT would be, at least in part, crossmodal effects caused by simultaneous exposure to the visual and haptic features of objects.…”