Averaging effects in spatial working memory do not depend on stored ensemble statistics

Recall from visual working memory shows averaging affects. For example, the recalled position of a memorised item is biased toward the average location of all items in a memory array. A recent suggestion is that averaging reflects an attempt to optimise single-item recall by exploiting ensemble statistics. This proposal predicts that the average location is memorised independently from that of individual items. We compared normal subjects� perceptual estimates of the centre of mass (COM) of three-stimulus dot arrays, COM from recall and single items from recall. Perceptual estimates of COM showed a systematic bias toward the array�s incenter, COM recall did not show this bias. The precision of COM recall was lower than COM perceptual estimates and higher than single item recall. In a right hemisphere patient with left hemianopia and neglect, COM perceptual estimates were systematically biased contralesionally, while COM recalls were biased ipsilesionally, confirming the dissociation between perception and recall. These findings suggest that COM is recalled by averaging the memorised items� positions rather than by retrieving its memorised perceptual estimate. Averaging in spatial recall may arise instead from a reference frame transformation, ensuring that the relative position of the item in the sample array is recalled

Lesions of the Medial Occipito-Temporal cortex affect spatial binding of sensory and memory data

Occipito-temporal cortex is parcellated, with medial regions having a greater representation of the visual periphery than regions along the lateral aspect. Imaging studies have suggested disparate functions for medial regions. These proposals do not generally account for the dramatic impairments of attention and memory displayed by patients with strokes in medial Occipito- Temporal cortex. We examined a middle-aged man, who had suffered bilateral posterior circulation strokes involving the medial Occipito-Temporal cortex. The patient showed impaired recognition of compound objects, when constituent parts were rearranged, but not, for example, when their shape was changed. The patient was impaired when recalling the color of an object from visual working memory, only when the object was identified by its location, rather than shape. He showed a specific liability to long recall delays, with an increase in spatial binding errors. The patient had no difficulty discriminating large and small objects, or performing a facial discrimination task, as long as the task did not require the appraisal of fine spatial relations between facial features. We conclude that medial Occipito�Temporal Cortex is crucial for spatial binding of perceptual and memory information, in part because of its role in maintaining stable spatial representations over time