Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dissociable Neural Subsystems Underlie Visual Working Memory for Abstract Categories and Specific Exemplars

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dissociable Neural Subsystems Underlie Visual Working Memory for Abstract Categories and Specific Exemplars

Article excerpt

An ongoing debate concerns whether visual object representations are relatively abstract, relatively specific, both abstract and specific within a unified system, or abstract and specific in separate and dissociable neural subsystems. Most of the evidence for the dissociable subsystems theory has come from experiments that used familiar shapes, and the usage of familiar shapes has allowed for alternative explanations for the results. Thus, we examined abstract and specific visual working memory when the stimuli were novel objects viewed for the first and only time. When participants judged whether cues and probes belonged to the same abstract visual category, they performed more accurately when the probes were presented directly to the left hemisphere than when they were presented directly to the right hemisphere. In contrast, when participants judged whether or not cues and probes were the same specific visual exemplar, they performed more accurately when the probes were presented directly to the right hemisphere than when they were presented directly to the left hemisphere. For the first time, results from experiments using visual working memory tasks support the dissociable subsystems theory.

The nature of representations of visual objects remains a topic of debate. Some theories posit that such representations are relatively abstract, in that a common representation may be activated by multiple exemplars or by multiple views of the same object exemplar (see, e.g., Biederman, 1987; Biederman & Bar, 1999; E. E. Cooper, Biederman, & Hummel, 1992; Hayworth & Biederman, 2006; Hummel & Biederman, 1992; Hummel & Stankiewicz, 1996; Wagemans, Van Gool, & Lamote, 1996). Other theories posit that object representations are relatively specific, in that different representations are activated by different exemplars or by different views of the same object exemplar (see, e.g., Bulthoff & Edelman, 1992; Gauthier et al., 2002; Poggio & Edelman, 1990; Tarr, 1995; Tarr & Gauthier, 1998; Tarr, Williams, Hayward, & Gauthier, 1998; Ullman, 1996). Alternatively, both abstract and specific representations may exist along different points on a continuum in a single, unified processing system (see, e.g., Farah, 1992; Hayward & Williams, 2000; Tarr & Bulthoff, 1995). Finally, abstract and specific object representations may exist in separate and dissociable neural subsystems, with an abstract subsystem operating effectively in the left hemisphere (LH) and a specific subsystem operating effectively in the right hemisphere (RH) (see, e.g., Burgund & Marsolek, 2000; Marsolek, 1995, 1999; Marsolek & Burgund, 1997, 2003).

The bulk of the evidence for the dissociable neural subsystems theory comes from experiments in which familiar shapes were used. This may be cause for concern, as Curby, Hayward, and Gauthier (2004) recently suggested, since abstract effects in the LH could reflect semantic processing of postvisual information that is associated with the visualshape information, rather than processing of (abstract) visual shapes only, as posited by the dissociable neural subsystems theory. A related concern is that abstract effects in the LH could reflect linguistic processing of names associated with the visual shapes, rather than processing of abstract visual-shape information. In addition, when objects are presented multiple times in an experiment, abstract effects in the LH could reflect episodic memory for previous trials in the experiment. In this article, we report results that indicate, in line with the dissociable neural subsystems theory, that abstract processing of visual shapes in the LH does not require semantic, linguistic, or episodic information. Abstract processing of visual shapes can occur effectively in the LH when the stimuli are novel objects viewed for the first and only time.

According to the dissociable neural subsystems theory, an abstract category subsystem and a specific exemplar subsystem operate relatively independently and in parallel. …

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