Neuroimaging tests of sensorimotor theories of semantic memory hinge on the extent to which similar activation patterns are observed during perception and retrieval of objects or object properties. The present study was motivated by the hypothesis that some of the seeming discrepancies across studies reflect flexibility in the systems responsible for conceptual and perceptual processing of color. Specifically, we test the hypothesis that retrieval of color knowledge can be influenced by both context (a task variable) and individual differences in cognitive style (a subject variable). In Experiment 1, we provide fMRI evidence for differential activity during color knowledge retrieval by having subjects perform a verbal task, in which context encouraged subjects to retrieve more- or less-detailed information about the colors of named common objects in a blocked experimental design. In the left fusiform, we found more activity during retrieval of more- versus less-detailed color knowledge. We also assessed preference for verbal or visual cognitive style, finding that brain activity in the left lingual gyrus significantly correlated with preference for a visual cognitive style. We replicated many of these effects in Experiment 2, in which stimuli were presented more quickly, in a random order, and in the auditory modality. This illustration of some of the factors that can influence color knowledge retrieval leads to the conclusion that tests of conceptual and perceptual overlap must consider variation in both of these processes.

We investigated dorsal visual stream involvement in the retrieval of a variety of visual attributes of common objects, using functional magnetic resonance imaging. Seven subjects made binary decisions about the shape, color, and size of named objects during scanning. Bilateral parietal activity was significantly greater during retrieval of shape and size information than during retrieval of color information. Consistent with a domain-specific distributed model of semantic organization, the finding that dorsal stream activity is associated with size and shape retrieval,as compared with color retrieval,may indicate that both size and shape information are learned partly through dorsally mediated processes, such as visually guided grasping. These results demonstrate that both visual-processing streams (i.e., the ventral "what" pathway and the dorsal "where" pathway) are involved in the storage and/or retrieval of knowledge of object appearance but that, just as in vision, these two pathways may play different roles in conceptual processing.

Numerous neuroimaging and neuropsychological studies have highlighted the role of the ventral, occipitotemporal visual processing stream in the representation and retrieval of semantic memory for the appearance of objects. Here, we examine the role of the parietal cortex in retrieval of object shape information. fMRI data were acquired as subjects listened to the names of common objects and made judgments about their shape. Recruitment of the left inferior parietal lobule (IPL) during shape retrieval was modulated by the amount of prior tactile experience associated with the objects. In addition, the same pattern of activity was observed in right postcentral gyrus, suggesting that the representation of object shape is distributed amongst regions that are relevant to the sensorimotor acquisition history of this attribute, as predicted by distributed models of semantic memory.

People with phonologic alexia often have difficulty reading functors and verbs, in addition to pseudowords. Friedman et al. [Friedman, R. B., Sample, D. M, & Lott, S. N. (2002). The role of level of representation in the use of paired associate learning for rehabilitation of alexia. Neuropsychologia, 40, 223-234] reported a successful treatment for phonologic alexia that paired problematic functors and verbs with easily read relays that were homophonous nouns (e.g. "be" paired with "bee"). The current study evaluates the efficacy of pairing problematic grammatical words with relays that share initial phonemes, but vary in the relationship of their final phonemes. Results showed that reading of target grammatical words improved to criterion level (90% accuracy over two consecutive probes) in all experimental conditions with shared phonology, but remained far below criterion level in control conditions. There was a significant correlation between degree of phonologic relatedness and error rate. Maintenance of the treatment effect was poor as assessed by traditional measurement, however a dramatic savings during relearning was demonstrated during a subsequent treatment phase. The finding that reading can be re-organized by pairing target words not only with homophones, but with other phonologically related relays, suggests that this approach could be applied to a wide corpus of words and, therefore, potentially be of great use clinically. We suggest, within a connectionist account, that the treatment effect results from relays priming the initial phonologic units of the targets.

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