Working Memory for Linguistic and Non-linguistic Manual Gestures: Evidence, Theory, and Application

We have used neuroimaging techniques, mainly positron emission tomography (PET), to study cognitively driven issues about working memory. Two kinds of experiments are described. In the first kind, we employ standard subtraction logic to uncover the basic components of working memory. These studies indicate that: (a) there are different working-memory systems for spatial, object, and verbal information (with the spatial system localized more in the right hemisphere, and the verbal system more in the left hemisphere); (b) within at least the spatial and verbal systems, separable components seem to be responsible for the passive storage of information and the active maintenance of information (with the storage component being localized more in the back of the brain, and the maintenance component in the front); and (c) there may be separate components responsible for processing the contents of working memory (localized in prefrontal cortex). In our second kind of experiment we have focused on verbal working memory and incrementally varied one task parameter-memory load-in an effort to obtain a more fine-grained analysis of the system's operations. The results indicate that all relevant components of the system show some increase in activity with increasing memory load (e.g., the frontal regions responsible for verbal rehearsal show incremental increases in activation with increasing memory load). In contrast, brain regions that are not part of the working-memory system show no effect of memory load. Furthermore, the time courses of activation may differ for regions that are sensitive to load versus those that are not. Taken together, our results provide support for certain cognitive models of working memory (e.g., Baddeley, 1992) and also suggest some distinctions that these models have not emphasized. And more fundamentally, the results provide a neural base for cognitive models of working memory.

When the brain is deprived of input from one sensory modality, it often compensates with supranormal performance in one or more of the intact sensory systems. In the absence of acoustic input, it has been proposed that cross-modal reorganization of deaf auditory cortex may provide the neural substrate mediating compensatory visual function. We tested this hypothesis using a battery of visual psychophysical tasks and found that congenitally deaf cats, compared with hearing cats, have superior localization in the peripheral field and lower visual movement detection thresholds. In the deaf cats, reversible deactivation of posterior auditory cortex selectively eliminated superior visual localization abilities, whereas deactivation of the dorsal auditory cortex eliminated superior visual motion detection. Our results indicate that enhanced visual performance in the deaf is caused by cross-modal reorganization of deaf auditory cortex and it is possible to localize individual visual functions in discrete portions of reorganized auditory cortex.

A general working memory system for ease of language understanding (ELU, Rönnberg, 2003a) is presented. The purpose of the system is to describe and predict the dynamic interplay between explicit and implicit cognitive functions, especially in conditions of poorly perceived or poorly specified linguistic signals. In relation to speech understanding, the system based on (1) the quality and precision of phonological representations in long-term memory, (2) phonologically mediated lexical access speed, and (3) explicit, storage, and processing resources. If there is a mismatch between phonological information extracted from the speech signal and the phonological information represented in long-term memory, the system is assumed to produce a mismatch signal that invokes explicit processing resources. In the present paper, we focus on four aspects of the model which have led to the current, updated version: the language generality assumption; the mismatch assumption; chronological age; and the episodic buffer function of rapid, automatic multimodal binding of phonology (RAMBPHO). We evaluate the language generality assumption in relation to sign language and speech, and the mismatch assumption in relation to signal processing in hearing aids. Further, we discuss the effects of chronological age and the implications of RAMBPHO.