Abstract
Previous psychophysical experiments with normal human observers have shown that adaptation to a moving dot stream causes directionally specific repulsion in the perceived angle of a subsequently viewed moving probe. In this study, we used a two-alternative forced choice task with roving pedestals to determine the conditions that are necessary and sufficient for producing directionally specific repulsion with compound adaptors, each of which contains two oppositely moving, differently colored component streams. Experiment 1 provided a demonstration of repulsion between single-component adaptors and probes moving at approximately 90° or 270°. In Experiment 2, oppositely moving dots in the adaptor were paired to preclude the appearance of motion. Nonetheless, repulsion remained strong when the angle between each probe stream and one component was approximately 30°. In Experiment 3, adapting dot pairs were kept stationary during their limited lifetimes. Their orientation content alone proved insufficient for producing repulsion. In Experiments 4–6, the angle between the probe and both adapting components was approximately 90° or 270°. Directional repulsion was found when observers were asked to visually track one of the adapting components (Exp. 6), but not when they were asked to attentionally track it (Exp. 5), nor while they passively viewed the adaptor (Exp. 4). Our results are consistent with a low-level mechanism for motion adaptation. This mechanism is not selective for stimulus color and is not susceptible to attentional modulation. The most likely cortical locus of adaptation is area V1.Electronic supplementary materialThe online version of this article (doi:10.3758/s13414-016-1160-1) contains supplementary material, which is available to authorized users.
Highlights
Previous psychophysical experiments with normal human observers have shown that adaptation to a moving dot stream causes directionally specific repulsion in the perceived angle of a subsequently viewed moving probe
Within the context of signal-detection theory (Green & Swets, 1966), the apparent directions of the two probes can be described by normal distributions S and T, such that S ~ N(p + μ, σ2/2) and T ~ N(p + t + μ, σ2/2), where σ2 is the variance of the performance-limiting noise, p and p + t represent the physical directions of drift, and μ represents any perceptual bias, such as may be induced by adaptation
The results of our Experiment 2 supported the claim by Blaser et al (2005) that motion adaptation can be produced by a paired-dot stimulus (Qian et al, 1994)
Summary
Previous psychophysical experiments with normal human observers have shown that adaptation to a moving dot stream causes directionally specific repulsion in the perceived angle of a subsequently viewed moving probe. Blaser et al used different colors for the leftward- and rightward-moving dots, and reported repulsion of red probes from red adaptors, and green from green.
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