Academic journal article Psychonomic Bulletin & Review

The Object Advantage Can Be Eliminated under Equiluminant Conditions

Academic journal article Psychonomic Bulletin & Review

The Object Advantage Can Be Eliminated under Equiluminant Conditions

Article excerpt

Published online: 4 April 2014

© Psychonomic Society, Inc. 2014

Abstract A key phenomenon supporting the existence of object-based attention is the object advantage, in which responses are faster for within-object, relative to equidistant between-object, shifts of attention. The origins of this effect have been variously ascribed to low-level "bottom-up" sensory processing and to a cognitive "top-down" strategy of within-object attention prioritization. The degree to which the object advantage depends on lower-level sensory processing was examined by differentially stimulating the magnocellular (M) and parvocellular (P) retino-geniculocortical visual pathways by using equiluminant and nonequiluminant conditions. We found that the object advantage can be eliminated when M activity is reduced using psychophysically equiluminant stimuli. This novel result in normal observers suggests that the origin of the object advantage is found in lower-level sensory processing rather than a general cognitive process, which should not be so sensitive to differential activation of the bottom-up P and M pathways. Eliminating the object advantage while maintaining a spatial-cueing advantage with reduced M activity suggests that the notion of independentM-driven spatial attention and P-driven object attention requires revision.

Keywords Space-based attention . Attention systems . Object-based attention . Cognitive neuroscience Perception

Psychophysical (e.g., Tipper, Weaver, Jerreat, & Burak, 1994), physiological (e.g., He, Humphreys, Fan, Chen, & Han, 2008), neuroimaging (e.g., Yantis & Serences, 2003), and nemo logical patient studies (e.g., Egly, Driver, & Rafal, 1994) have established the existence of distinct space-based (also referred to as location-based) and object-based attention effects. A key paradigm-which involves a pair of two- dimensional rectangles as objects, spatial cueing, and a simple reaction time (RT) response (e.g., Brown, Breitmeyer, Leighty, & Denney, 2006; Egly et al., 1994)-has generated a substantial literature showing an advantage for shifting attention within an object, as compared to equidistant shifts between two objects. The object advantage has been consid- ered evidence of the facilitative, bottom-up effect of object- based attention guiding the spread of attention (e.g., Brown et al., 2006) or a top-down effect reflecting a prioritization of within- relative to between-object shifts of attention (Shomstein & Yantis, 2002, 2004). It has also been shown that disengaging and shifting object-based attention away from a cued object, whether to another object or to a location, is a factor contributing to the object advantage (Brown & Denney, 2007).

In the present experiments, we sought to disambiguate these two explanations by presenting an otherwise identical version of the task with equiluminant and nonequiluminant chromatic stimuli. Equiluminant stimuli would selectively reduce magnocellular- (M-) driven responses that show poor sensitivity to wavelength (Livingstone & Hubel, 1987).1 M- driven responses are thought to be the dominant initial input to the dorsal, "Where" stream (see, e.g., Merigan & Maunsell, 1993), as compared with parvocellular- (P-) driven responses, which are thought to provide the dominant initial input to the "What" stream (Haxby et al., 1991; Ungerleider & Haxby, 1994). If the phenomenon of the object advantage were main- ly a result of a top-down strategy, we would expect little change If the size of the object advantage relative to valid spatial cueing (regardless of any change in the absolute RT magnitude), because the P-driven responses are perfectly ca- pable of generating an object percept (Yantis & Hillstrom, 1994). Thus, according to a top-down prioritization account, no differences should emerge in the size of either the object advantage or the validity effect (i.e., valid RTs that are signif- icantly shorter than invalid RTs) between equiluminant and nonequiluminant conditions. …

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