Role of the right temporal lobe in visual-cue learning during repeated pattern discriminations

The ability to acquire visual cues for discriminating between two targets against a background of visually similar items was examined in 64 patients with unilateral temporal- or frontal-lobe excisions and 20 normal control subjects. The subjects were tested on two versions (letters and abstract designs) of a visual cue-learning task that was an adaptation and extension of RABBITT's (Am. J. Psychol. 80, 1-13, 1967) visual-search paradigm. For both versions, the material consisted of two packs of cards, each containing a different set of background letters or designs. Subjects were required to sort the cards into two piles according to which of two targets was present on the card. On the letter task, all groups took longer to sort when the background letters were changed after three learning trials. With abstract designs, patients with right temporal-lobe lesions failed to show this interference effect after three learning trials, but they, like other groups, did so after six. This slowness in learning was related neither to the extent of hippocampal removal nor to visual-field defects. It is argued that the right temporal neocortex plays a role in incremental learning of visual cues during repeated pattern discriminations.