Abstract
The presence of neural mechanisms selective to particular combinations of Fourier energies, namely plaids, have previously been shown through a compound adaptation procedure (Peirce and Taylor, 2006). Rather than responding to individual sinusoidal gratings, these mechanisms respond to particular conjunctions of them. Using a similar, but simpler, method we investigated the role of probe contrast in the compound adaptation effect. Subjects were adapted to two alternating component gratings in one visual hemi-field; while a plaid, constructed of the same components presented together, was adapted in the other hemi-field. Subjects then compared the contrast of a probe at the same retinal location of the compound adaptor (test probe) with one at the location of the component adaptors (reference probe). An adaptive staircase homed in on the point of subjective equality (PSE) for contrast at these two locations. Reference probes took one of 5 fixed contrast values, ranging between 0.15 and 0.6. Our results indicate that the compound adaptation effect was strongest when the reference probe's Michelson contrast fell between 0.2 and 0.3, consistent with a plaid-selective mechanism, whose contrast response function rises most steeply in this region.
BBSRC grant held by JWP (BB/C50289X/1)