Cite as:
Olzak L A, Saylor S A, Laurinen P I, 2003, "What stops lateral interactions in pattern discrimination tasks?" Perception 32 ECVP Abstract Supplement
What stops lateral interactions in pattern discrimination tasks?
L A Olzak, S A Saylor, P I Laurinen
In previous research, we demonstrated that surround patterns reduce the ability to make fine spatial discriminations on centre patterns in ways consistent with interactions among low-level mechanisms. If, however, the centre and surround are out of phase with one another, or even a tiny gap of mean luminance is introduced between centre and surround, all suppressive effects disappear. Here, we asked whether the disappearance of suppressive effects was primarily due to low-level effects (ie among spatially very localised or only among V1-like mechanisms of the same phase), or whether mechanisms of scene segregation or attention also reduced suppressive effects. We segregated centre and surround in test conditions by changing the relative mean luminance of the centre and surround. Patterns to be discriminated were two patches of near-vertical sinusoids of 3 cycles deg-1, displayed in a sharp-edged 40 min of arc window that differed slightly in orientation. In control conditions, surrounds were unmodulated and of the same mean luminance as the centre pattern (either 11.2 or 19.8 cd m-2). A second pair of controls was run with high-luminance centres and unmodulated low-luminance surrounds, and vice versa. Performance (d') was slightly reduced from original controls when luminances did not match. In test conditions, the surround was modulated (3 cycles deg-1 vertical sinusoid) around either high or low mean luminance value. All four combinations of centre and surround luminance were tested. When surrounds were modulated and of equal luminance, performance was near chance. Segregation by changes in luminance reduced the suppressive effects of modulation, although to differing degrees in different observers. We conclude that higher-level processes can modulate lateral interactions.
[Supported by NIH grant EY13953 to LAO.]
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