Contextual effects on decision templates for parafoveal orientation identification.
When a peripherally viewed stimulus is presented with flankers, observers' acuity for shape generally decreases. We wondered whether a change in the locus of information accrual accompanied these performance deficits and employed psychophysical reverse correlation to find out. Surrounding the target (a near-vertical Gabor patch) with a vertical grating caused a slight elongation and a rotation in the decision templates for orientation identification. We also found that the contrast required to maintain criterion performance in this condition was actually lower than it was in a target-alone condition. However, this facilitation decreased with practice, due to perceptual learning in the target-alone condition. Unlike a continuous surround, isolated flanks elevated contrast thresholds, but decision templates were similar with both of these contexts. The rotation of decision templates (off-orientation looking) suggests that performance is limited by additive internal noise. We speculate that this noise can be reduced when the target is easily segregated from its surround.
Mareschal
Isabelle
I
Department of Optometry and Visual Science, City University, London EC1V 0HB, UK. Isabelle.Mareschal.1@city.ac.uk
Morgan
Michael J
MJ
Solomon
Joshua A
JA
D015350:Contrast Sensitivity / Q000502:physiology; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D005584:Fovea Centralis / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D009949:Orientation; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology