Figure 1.

SRP. A, Schematic of experimental apparatus. VEPs were recorded from layer 4 of binocular primary visual cortex (V1). B, Time course of experiments described within Figure 1. Mice were implanted with recording electrodes and head post was affixed at P30. On recovery, mice were habituated to the apparatus on 2 consecutive days. Over the next 5 d, VEPs were sampled, each driven by a 0.5 Hz phase-reversing, full-field, 0.05 cycle/°, 100% contrast, sinusoidal grating stimulus, of X° orientation, and averaged each day (gray squares). On the final day, VEPs were evoked by a multitude of other stimuli, varying in spatial frequency, contrast, and orientation (D, white circles). C, The averaged trough–peak VEP amplitude driven by X° increased significantly over days, reaching asymptote on day 5 (n = 7). D, VEPs driven by novel stimuli equivalent in all regards except being as little as 5° different in orientation from familiar X° (white circles), were significantly lower amplitude than those driven by X°. VEP amplitude is here presented as a percentage of those driven by an orthogonal orientation (X + 90°, dotted horizontal line at 100%). VEPs driven by orientations similar to X° were greater amplitude than X + 90°-driven VEPs out to a boundary of around X ± 25° (n = 7). E, Averaged VEPs driven by stimuli varying in spatial frequency, from 0.15 to 0.6 cycle/°, were equivalent in amplitude for either the familiar X° (gray squares) or unfamiliar X + 90° stimulus (white circles) on day 5. Only at the familiar spatial frequency of 0.05 cycle/° did X° evoke a significantly larger VEP than X + 90° (n = 8). F, Averaged VEPs driven on day 5 by stimuli varying in contrast are equivalent in amplitude for either familiar X° (gray squares) or unfamiliar X + 90° (white circles) for all contrast values other than the familiar 100% contrast, at which X° evoked significantly greater amplitude VEPs than X + 90°. Error bars in all graphs are SEM. Example VEPs are presented for each day above the relevant graph point for C–F. Calibration: vertical, 100 μV; horizontal, 50 ms. VEP traces represent an average of 200 EEG samples after visual stimulus phase reversal. Traces run from phase reversal onset, such that the average response onset is ∼25 ms and the average peak negativity is ∼50 ms after visual stimulus phase reversal. Asterisks represent statistical comparisons yielding a significant difference (p < 0.05).