Abstract
Previous research (Guenther & Brown, VSS 2008) comparing the effect of stimulus ramping on inhibition of return (IOR) failed to find significant differences between abrupt and ramped conditions when objects were not present in the display. Only when 2-D outline or 3-D cube shaped objects were added to the display did an effect of stimulus ramping emerge. It is possible the absence of a ramping effect without objects could be due to the duration of the ramp used (106 ms). Other studies have used longer ramping durations (200–250 ms) to generate P-biased conditions (e.g., Breitmeyer & Julesz, 1975; Tolhurst, 1975). The present experiments used a longer ramping duration (212 ms). Experiment 1 compared conditions with and without 2-D objects and found strong ramping based effects on IOR in both conditions. In Experiment 1 (as in Guenther & Brown, VSS 2008) abrupt cues were paired with abrupt targets and ramped cues with ramped targets. Therefore, it was possible the observed ramping effects were due to the ramped cues instead of the targets. To rule out this possibility, Experiment 2 compared responses to ramped targets paired with abrupt cues and abrupt targets paired with ramped cues. Across both experiments, IOR magnitude increased for ramped compared to abrupt targets irrespective of cue type. The present experiments illustrate the importance of sensory influences on IOR and support previous research (Guenther & Brown, VSS 2007, VSS 2008; Guenther, Brown, Narang, & Siddiqui, VSS 2009) suggesting stimuli biased towards the parvocellular pathway produce greater IOR than stimuli biased towards the magnocellular pathway.