Relative motion induced between stationary lines.

Simple harmonic motion of two moving tines can induce a relative motion between two adjacent stationary lines. There is both a maximum and minimum stimulus amplitude within which this motion can be seen and this depends on frequency. For a wide range of low frequencies the lower amplitude limit for induced motion is inversely proportional to frequency, suggesting that the phenomenon requires a minimum threshold velocity independent of amplitude. Furthermore, there is a relatively steep high frequency cut-off in the lower limit of induced motion. occurring between Z and 5 Hz. which is a much lower frequency than that for real motion. The upper amplitude limit for induced motion has an entirely different characteristic (slope of -2 on log-log coordinates). indictiing that the upper limit is not limited by velocity alone but by both velocity and amplitude. In comparison to real motion. the upper velocity limit for movements of 1” or less is very low (less than I’/sec). Subsidiary experiments using constant velocity stimuli support the above conclusions. The results are interpreted in terms of hypothetical velocity-sensitive neurons having a center surround organization with respect to velocity and a range of receptive field sizes. with preferred velocity increasing for increasing field sizes.