Visual Learning and Imagery

It has been hypothesized that cortical areas involved in visual perception are also involved in the recall of images. This hypothesis has been tested using both fMRI and PET. In one study, subjects alternately viewed LED displays of flashing squares or were asked to imagine the display pattern. A region of high activity during the stimulation condition was observed in the posterior occipital cortex that was reported to include both areas V1 and V2. This same region showed strong, yet weaker activation during the imagine condition in five of the seven subjects tested. These results suggest that areas V1 and V2 are involved in the recall or imagination of visual stimuli.

A second study reached a different conclusion using a different paradigm that allowed the assessment of the role of various cortical regions in visual learning, recall, and recognition. Subjects were presented various colored geometric patterns and were tested for their learning of the pattern contents. PET imaging was used to assess the cortical regions involved in the learning phase as well as in the recall and recognition of these learned patterns. Due to the limited spatial resolution of the PET method and the lack of topographic mapping in these experiments, it was not possible to assign activation foci to specific cortical areas. However, it was possible to compare the activations across learning, recall, and recognition conditions. Early cortical area V1 and adjacent pericalcarine areas (such as V2) were activated in the learning phase of this experiment. In contrast, no cortical regions in the occipital lobe were activated significantly during the recall of learned patterns. In addition, V1 and adjacent pericalcarine fields were activated during the recognition task, where learned patterns were presented intermixed with similar novel patterns. These results suggest that areas V1 and V2 are not involved in visual recall, but instead higher cortical and limbic areas are involved in this complex process. The differences in the results between this study and the first study appear substantial and may be attributable to methodological differences.

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