The steady/pulsed-pedestal paradigm has been shown to be an effective manipulation of relative magnocellular (M) and parvocellular (P) activity (e.g., Leonova, Pokorny, & Smith, 2003; McAnany & Levine, 2007). However, this manipulation has primarily been used with contrast sensitivity measures. The purposes of the present study were to evaluate the effectiveness of this manipulation using a simple reaction time (RT) measure and then test previous findings showing specific influences on space- and object-based attention under M- and P-biased conditions. Cuing studies investigating object-based attention have shown the cost for shifting attention within an object is less than equidistant shifts between two objects (object advantage = within-object RTs between-object RTs). We previously reported this object advantage is eliminated under equiluminant (P-biased) conditions because of increased within-object RTs (Boyd, Guenther, & Brown, VSS 2007). The first experiment measured simple RTs to a square target presented at center screen on a square pedestal (20% catch trials) to see if the pulsed-pedestal would cause increased RTs expected from P-biased conditions. The steady/pulsed-pedestal manipulation produced reliable differences in RTs consistent with M- and P-biased conditions with overall RTs longer for the pulsed (P-biased) compared to the steady (M-biased) pedestal condition. A second experiment tested for an object advantage using pairs of rectangular bars (tilted 45?° left or right of vertical) as objects. Again overall RTs were greater for pulsed compared to steady pedestal conditions. A similar magnitude validity effect (valid RTs invalid RTs) was found for both conditions indicating that, in general, the pulsed condition did not interfere with shifting attention. However, the pulsed condition had a greater influence on RTs for within- compared to between-object shifts. Similar to our previous study, RTs for within-object shifts increased for P-biased conditions eliminating the object advantage.
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