Deficits in egocentric-updating and spatial context memory in a case of developmental amnesia.

Patients with developmental amnesia usually suffer from both episodic and spatial memory deficits. DM, a developmental amnesic, was impaired in her ability to process self-motion (i.e., idiothetic) information while her ability to process external stable landmarks (i.e., allothetic) was preserved when no self-motion processing was required. On a naturalistic and incidental episodic task, DM was severely and predictably impaired on both free and cued recall tasks. Interestingly, when cued, she was more impaired at recalling spatial context than factual or temporal information. Theoretical implications of that co-occurrence of deficits and those dissociations are discussed and testable cerebral hypothesis are proposed.

Hemisphere specialisation and inter-hemispheric cooperation during a phonological task: effect of lexicality as assessed by the divided visual field approach.

In the presented experiment we explored the effect of lexicality on hemisphere specialisation and cooperation during a phonological task. The divided visual field (DVF) method with bilateral presentation (BVF) of redundant (identical) stimuli is considered an appropriate approach to assess inter-hemispheric cooperation (IHC). IHC is supposed to increase the efficiency of cognitive processes. Specifically, it has been shown that, compared to unilateral hemifield presentation, word processing is significantly more efficient if stimuli were presented under bilateral redundancy conditions. The performance enhancement during bilateral vs. unilateral presentation is called bilateral redundant gain (BRG). In the present experiment a DVF was used and participants were required to perform a rhyme detection task in two blocks, one in words and another one in pseudowords. Each item was presented in two different modes, one unilateral (right or left hemi-visual field) and another one bilateral (simultaneous redundant presentation). Unilateral trials allow one to study hemispheric specialisation, while bilateral redundant trials allow one to study inter-hemispheric cooperation. We obtained left hemisphere specialisation for both types of items (word, pseudoword). Moreover, words were more efficiently processed than pseudowords. Additionally, words were processed more efficiently in BVF than in unilateral presentation, inducing BRG. No similar effect was obtained for pseudowords. These results are discussed in respect to findings reported by other studies suggesting that hemispheric specialisation depends on lexicality. Moreover, compared to lexical decision tasks used in previous studies, the phonological task used in the present study seems to modulate the inter-hemispheric cooperation less.