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Two experiments were carried out to investigate duration estimation of rotating-spot-patterns under a situation with the minimum cue to frequency. Twenty-four undergraduates were used as subjects in each experiment. The magnitude estimation method was used in Experiment I, where for a constant duration, the estimate of the duration increased with the velocity of the rotation of the pattern except for that of stationary pattern, where the duration was estimated longer than that for the slowest of the moving patterns. The same tendencies were observed in Experiment II, where the magnitude production method was used. The multiple regression analysis suggested that the best model which explains the velocity effects upon time estimation was a multiplicative one and contained a quadratic function of logarithmically transformed velocity in both experiments. The explanatory principles of the velocity effects and the validity of the model were discussed in the light of past studies.

2. The action spectrum of the response obtained in this way agrees reasonably well with the observer's psychophysical foveal luminosity curve.3. For the peripheral retina, the action spectrum is similar to that of the fovea when allowance is made for differences in screening macular pigment.4. Such responses diminish when the test stimulus is focused on to the peripheral retina and disappear when the test light is focused on the blind spot.5. Therefore, the response to the test light fixated centrally is the result of the excitation only of cones mainly, if not exclusively, in the fovea.6. When the intensity of the background is reduced by a factor of 10, the action spectrum shows evidence of the effect of excitation of rods in the blue part of the spectrum and of cones in the red. These red and blue responses add linearly when combined together, provided they are adjusted to coincide in phase.

Observers viewed animation sequences consisting of random dots, some of which moved coherently in a given direction (signal dots) and the rest of which moved randomly (noise dots). Using forced‐choice procedures, detectability of weak signals within noise was measured for translation, rotation, and expansion/contraction. Sensitivity to all motion types was approximately equal, with practiced observers reliably detecting coherent motion at signal levels as low as 4%. Observers were able to identify the motion structure presented on a given trial at signal levels corresponding to the detection threshold, implying that the neural signals supporting detection are labeled for motion type. Results are discussed in the context of hierarchical analysis of optic flow in which all motion types are registered as patterns of activity among neurons comprising a single mechanism.