Isolating Excitatory and Inhibitory Nonlinear Spatial Interaction
Involved in Contrast Detection.
Zenger B. &
Sagi D. (1996).
Vision Research
36, pp. 2497-2513
Interactions between filters tuned to different orientations and
spatial locations were investigated with a masking paradigm. Targets
were masked by pairs of Gabor signals presented either at a different
orientation (+- Delta theta) or at a different spatial location (+-
Delta y). The two mask components were either of equal phase or of
opposite phase to each other. Detection thresholds of the target were
measured as a function of mask contrast. Typically, the curves
obtained showed the following behavior: for increasing mask contrast
the threshold first decreased, then reached a minimum and then
increased linearly on a log-log scale reflecting a power-law behavior.
Mask pairs of equal phase as well as opposite phasewere shown to
facilitate detection. Facilitation by mask pairs of equal phase was
larger (up to 0.4 log units) and decreased for increasing Delta theta
and Delta y. The facilitation for mask pairs of opposite phase (~0.1
log units) was observed only for larger Delta theta and Delta y. Phase
independent suppression was observed with higher mask contrasts at
smaller Delta theta and Delta y. The strength of this suppression was
shown to decrease with practice. We account for the observed
facilitation with an accelerating transducer function applied on a
second-stage filter. Suppression is modeled with an additional
inhibitory second stage filter that divides the output of this
transducer. Selective reduction of the inhibitory gain accounts for
the practice effects.
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