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Megan C. Boyd, Benjamin A. Guenther, James M. Brown; Investigating the role of the magnocellular pathway in object- and location-based attention. Journal of Vision 2007;7(9):1078. doi: 10.1167/7.9.1078.
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Purpose: Studies of spatial and temporal resolution have indicated covertly cuing visual attention emphasizes parvocellular (P) relative to magnocellular (M) processing at cued locations and P on M inhibition at those locations. Cuing studies investigating object-based attention have shown the cost for shifting attention between objects is greater than for equidistant shifts within objects and that this object effect may be due, in part, to disengaging object-based attention from one object to shift to another. We explored whether P on M inhibition may contribute to the disadvantage for shifting attention between objects by comparing achromatic conditions with equiluminant and diffuse red light background conditions expected to inhibit M pathway activity. If the object effect is due, in part, to P on M inhibition related to disengaging attention, then the object effect may be less under conditions where M activity is reduced. Method: Objects were pairs of rectangular bars presented vertically and horizontally. Cues and targets appeared at the ends of the bars and were equidistant from a fixation point. Targets appeared 80% of the trials, and trials where targets appeared were valid 60% of the time. White-on-black (Exp. 1), black-on-red & black-on-green background (Exp. 2), and psychophysically equiluminant red-on-green and green-on-red (Exp. 3) conditions were tested. Results: Overall reaction times were longer under psychophysically equiluminant conditions indicating reduced M activity. The object effect for the achromatic condition (Exp 1) was two times that found in the equiluminant and red background conditions. Conclusion: The object effect was greatest under conditions where P on M inhibition related to attention would be the greatest. The difficulty shifting between objects was lessened under conditions where M activity was reduced, therefore decreasing the opportunity for P on M inhibition. The results suggest P on M inhibition plays a role in disengaging object-based attention.
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