Rw. Bowen et H. Derudder, DYNAMIC CONTRAST PERCEPTION ASSESSED BY PATTERN MASKING, Journal of the Optical Society of America. A, Optics, image science,and vision., 15(3), 1998, pp. 570-578
The perceived contrast of a pulsed grating varies markedly with the ex
posure duration and spatial frequency of the grating. We studied dynam
ic changes in perceived grating contrast with a pattern-masking paradi
gm. We measured masking of a brief, localized test pattern (a D6 stimu
lus, 30 ms in duration) by fixed-contrast cosine grating patterns of v
arying duration (50-500 ms). The cosine mask pattern had spatial frequ
ency of either 1 or 6 cycles per degree (cpd) at a contrast of 0.3. Th
e D6 test pattern was centered on a light bar of the mask and was eith
er positive peak contrast (same-polarity test and mask) or negative pe
ak contrast (opposite-polarity test and mask). In Experiment I, the te
st and mask had simultaneous onset. With a 6-cpd mask, the same-polari
ty test-threshold elevation versus mask-duration function increases mo
notonically. For a 1-cpd mask, the same-polarity threshold-mask-durati
on function is nonmonotonic, with peak masking effect produced by a gr
ating pulse of 80-100 ms. These masking effects are closely congruent
with known dynamic contrast effects. With negative tests, masking-dura
tion functions are elevated from same-polarity functions and are essen
tially similar in shape for 1- and 6-cpd masks. The elevated threshold
s suggest inhibitory interaction between ON and OFF pathways, with a s
imilar time course across spatial frequency. In Experiment 2, the D6 t
est was delayed from mask onset by 33 ms. Positive contrasts only were
employed. For 1-cpd stimuli, the delay of test greatly reduced maskin
g at all mask durations and eliminated the nonmonotonic function. This
suggests that for low-spatial-frequency patterns, perceived contrast
is determined by an early peak component of the neural response. But f
or 6-cpd stimuli, masking of the delayed test was somewhat greater at
all mask durations, consistent with a gradually increasing underlying
neural response to the grating. Finally, in Experiment 3, same-polarit
y masking effects at both spatial frequencies were replicated with neg
ative-contrast test and mask (OFF pathway mediation). This indicates t
hat the ON and OFF pathways have similar response dynamics. (C) 1998 O
ptical Society of America.