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Ling Lin, George Sperling; No iconic memory decay nor visual short-term memory decay for grating contrast. Journal of Vision 2008;8(6):206. doi: 10.1167/8.6.206.
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© ARVO (1962-2015); The Authors (2016-present)
Lu, Williamson and Kaufman (Science, 258, 1668–1669, 1992) determined exponential decay constants (between 1–3 sec) for auditory echoic memory for loudness (around 85 dB) of pure sine tones. Their listeners' echoic memories decayed to intermediate auditory memories of the context—the average loudness of all the tones presented in a session—in 2–6 sec, and were maintained for up to 12 sec. We explicitly followed Lu et al's paradigm intending to measure the decay of iconic memory of the contrast amplitude of a visual windowed sinewave grating (a Gabor patch) and also to create (as did Lu et al, 1992) different intermediate-term memories by varying the composition of all the stimuli in the session (context). To a good approximation we found that observers' judgments of relative contrast were as accurate for successive Gabor patches as for simultaneous stimuli, i.e., there was no iconic decay, nor was there any significant short-term memory decay over a delay period of up to 7 sec. This almost perfect memory of the encoded value of a Gabor patch's contrast is indicated by both stable mean values of observers' responses (point of subjective equality) and by stable variances of their responses. Experimental procedures: A broad-bandwidth Gabor patch of contrast 0.42 (in HIGH context condition) or 0.62 (in LOW context condition) was displayed for 267 msec, followed by a second Gabor patch whose contrast was randomly chosen between 0.36 and 0.68 which was displayed after a variable delay between 0 and 7.3 sec. Observers judge whether patch 2 has higher or lower contrast than patch 1. The session mean contrast is 0.47 in HIGH sessions and 0.57 in LOW sessions.
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