Academic journal article Perception and Psychophysics

Remembering "What" Brings along "Where" in Visual Working Memory

Academic journal article Perception and Psychophysics

Remembering "What" Brings along "Where" in Visual Working Memory

Article excerpt

Does a behavioral and anatomical division exist between spatial and object working memory? In this article, we explore this question by testing human participants in simple visual working memory tasks. We compared a condition in which there was no location change with conditions in which absolute location change and absolute plus relative location change were manipulated. The results showed that object memory was influenced by memory for relative but not for absolute location information. Furthermore, we demonstrated that relative space can be specified by a salient surrounding box or by distractor objects with no touching surfaces. Verbal memory was not influenced by any type of spatial information. Taken together, these results indicate that memory for "where" influences memory for "what." We propose that there is an asymmetry in memory according to which object memory always contains location information.

One of the most influential findings in cognitive neuroscience is that there is a division of labor in visual processing into what are colloquially known as "what" and "where" processing. These types of information are carried by two different neural processing streams, one ventral, the other dorsal. This anatomical division is thought to govern the neural workings of visual perception: The ventral stream is used for perceiving the identity of items, and the dorsal stream for perceiving where items are located in space (Ungerleider & Mishkin, 1982; see also Milner & Goodale, 1995).

The ventral stream begins in primary visual cortex (V1) and travels through inferior temporal cortex. The dorsal stream also begins in V1, but it travels a more superior route through posterior parietal cortex (Livingstone & Hubel, 1988; Mishkin, Ungerleider, & Macko, 1983). It has been theorized that this anatomical and cognitive division continues to some degree into the frontal lobes and influences how the frontal lobes process working memory information. Single-unit recordings in the frontal lobes of nonhuman primates suggest that areas in dorsal prefrontal cortex respond selectively to the maintenance of location information in visual working memory (VWM). Neurons that are more lateral and ventral, on the inferior prefrontal convexity, respond selectively to the maintenance of object or featural information (Chafee & Goldman-Rakic, 1998; Funahashi, Bruce, & Goldman-Rakic, 1989, 1990; O'Scalaidhe, Wilson, & Goldman-Rakic, 1999; Wilson, O'Scalaidhe, & Goldman-Rakic, 1993).

These findings have been the impetus for numerous neuroimaging studies of working memory for location versus identity or featural qualities of items. Although this field has been popular for research in neuroimaging, the data are highly inconsistent. Many studies report a dorsalventral segregation of working memory processes (Baker, Frith, Frackowiak, & Dolan, 1996; Courtney, Ungerleider, Keil, & Haxby, 1996; Haxby, Petit, Ungerleider, & Courtney, 2000; Smith, Jonides, Koeppe, Awh, Schumacher, & Minoshima, 1995), but a significant number of experiments do not find such segregation (D'Esposito, Ballard, Zarahn, & Aguirre, 2000; Nystrom et al, 2000; Postle, Stern, Rosen, & Corkin, 2000).

Researchers have offered a number of explanations for the inconsistencies found in neuroimaging experiments. Some (e.g., Nystrom et al., 2000; Postle & D'Esposito, 2000) have suggested that some neural regions in prefrontal cortex are not organized by stimulus modality but rather by type of processing (i.e., by processing rather than by the nature of the information being processed; Stern et al., 2000). Others have argued that objects may be a "representational middle ground," (e.g., Marshuetz & Bates, 2004) containing both spatial and object properties, or that the object and spatial memory results may be clouded because sometimes objects or spatial locations are verbalizable (e.g., Fletcher & Henson, 2001). …

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