The method of cued visual selection (CVS) was used to measure the identification speed of targets in different surrounds. Local orientation contrast is known to modulate neural responses in the visual system; we should expect targets with orientation contrast being faster identified than targets surrounded by similar lines. This was confirmed in the data of five (of six) observers in the main experiment of the study. Performances were measured with line arrays in which individual lines ("targets") were cued at various delays after stimulus onset. At all tested cue delays from 100 ms to 5 s after stimulus onset, targets in popout configurations were faster identified than cued targets in uniform configurations. At shorter delays (0 ms and 50 ms), differences were absent or not significant. Targets in border-like configurations, which 37.5% of the orientation contrast of popout targets, were identified at intermediate rates. Surrounds also affected the time course of growing target identification with increasing presentation time (after the cue), basically confirming predictions made from neural population responses at various delays after stimulus onset. The sixth subject behaved differently and produced opposite results. It was conjectured that this might have been due to crowding and an inability to quickly identify targets at the tested eccentricity. To test this hypothesis, this and two other subjects were tested in a modified experiment, in which target eccentricity was reduced and cued targets were presented closer to the fixation spot. This modification was sufficient to generate performance differences similar to those obtained with the other observers in the main experiment. Altogether, the experiments have uncovered perceptual variations in target identification that were predicted from neuronal response differences between uniform and popout targets. CVS has thus been proven a useful method for looking into details of neural processing in the visual system with psychophysical methods.

Published online: 18-Dec-2017

Citation: Nothdurft, H.C. (2017). Cued visual selection of targets with and without orientation contrast. VPL-reports, 7, 1-22, www.vpl-reports.de/7/