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Benjamin R. Stephens, James L. Dannemiller; Decruitment effects for magnitude estimates of pattern contrast. Journal of Vision 2002;2(7):194. doi: 10.1167/2.7.194.
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Teghtsoonian et al (Perception and Psychophysics, 2000) report that magnitude estimates for loudness of a very weak tone are much lower when the tone is presented at the end of a slowly and continuously decreasing intensity sweep compared to a presentation at the beginning of a continuously increasing intensity sweep. This decruitment effect was also reported for visual perceived size of a very small disk. Neuhoff (Nature, 1998) proposed that decruitment of loudness and perceived size may promote attention to approaching rather than receding targets. The current experiment attempts to replicate decruitment effects for perceived contrast and examine possible adaptation mechanisms for the effects. Naïve subjects (n=18) used a 100-point scale in a magnitude estimation procedure. Targets were 1.0 and 4.0 cpd stationary squarewave gratings. In each trial, the grating's contrast was increased or decreased logarithmically over a 45 sec sweep, with start or end points of 0.2 and 0.006 contrast. Subjects provided magnitude estimates, cued by a tone, during a sweep for four contrasts (0.1, 0.07, 0.01, and 0.007). Half of the trials presented a single spatial frequency, and half presented a sudden shift in frequency (to 4cpd or 1 cpd) 2 sec before the 0.01 contrast probe. For trials with no frequency shift, evidence of decruitment was observed: magnitude estimates for the 0.01 contrast targets were roughly a factor of two lower (p<0.05) when presented in the decreasing compared to the increasing sweep conditions. Similar decruitment effects were observed in the frequency shift condition, suggesting little or no adaptation effects. A second experiment (with frequency shifts coincident with the 0.01 probe contrast) replicated the results of the first experiment, indicating that the absence of adaptation effects was not due to the 2 sec delay prior to probed contrast. The impact of response bias, sensory, and higher-level mechanisms in decruitment will be discussed.
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