Über die Wirkung modalitätsspezifischer Hinweisreize im ikonischen Gedächtnis

Abstract

This study demonstrates a modality effect in relation to a cue used in experiments on iconic memory (visual sensory memory). Using a "partial report" paradigm, poorer reproduction was found with visual cues compared to auditory ones. In the study reported in this thesis, a neuropsychological model was developed to explain this effect and in addition, to enable a reconciliation between different existing theories of iconic memory. The model is based on the widely accepted assumption of two visual systems, whose anatomical substrates are taken to be the ventral path to the inferior temporal cortex and the dorsal path to the posterior parietal cortex, which first of all process visual information in parallel pathways corresponding to the attributes of "what" and "where", respectively. In this model, both kinds of information come together in a temporary buffer (which is assumed to be located in the superior temporal sulcus), where they are integrated and identified, under the active control of components of the prefrontal cortex. At the same time, these components of the prefrontal cortex also play an important role in the control of attention throughout the whole period of information processing. With the aid of the thalamic system (the pulvinar), attentional intent deriving from the prefrontal component(s) is implemented in selection during various phases of processing. Behavioral data, the reproduction performance in the cue modality experiments, support two assumptions of the model: (1) the recognition of objects in the ventral tract can proceed in parallel, but is limited in relation to perceptual capacity, and (2) the integration and identification of separately processed information in the temporary buffer is subject to limitations of cognitive capacity, as integration and identification can only be effected there in series. Experiments designed to test the model show that, on the one hand, the effect of cue modality in the Sperling paradigm can be attributed to perceptual interference resulting from a limitation on perceptual capacity in the ventral coding process (whole report condition) and, on the other, to processing conflict, due to a cognitive capacity limitation during integration and identification (partial report condition), as a result of the additional requirement of processing the visual cue stimulus in the same pathways. Moreover, the two separate information-processing pathways appear to have different properties. While the ventral tract is subject to a perceptual capacity limitation, the dorsal pathway is relatively free of this restriction, but is sensitive to temporal aspects. These different properties were reflected in different kinds of errors (identity errors vs. location errors) in the memory experiments. This new view of iconic memory, taken together with other visual phenomena and forms of memory, support the hypothesis of a unitary underlying information processing system with the same processing mechanisms.