Sensitive calibration and measurement procedures based on the amplification principle in motion perception

We compare two types of sampled motion stimuli: ordinary periodic displays with modulation amplitude m(o=e) that translate 90 degrees between successi ve frames and amplifier sandwich displays. In sandwich displays, even-numbe red frames are of one type, odd-numbered frames are of the same or differen t type, and (1) both types have the same period, (2) translate in a consist ent direction 90 degrees between frames, and (3) even frames have modulatio n amplitude m(e), odd frames have modulation amplitude m(o). In both first- order motion (van Santen, J.P.H. & Sperling, G. (1984). Temporal covariance model of human motion perception. Journal of the Optical Society of Americ a A, 1, 451-73) and second-order motion (Werkhoven, P., Sperling, G., & Chu bb, C. (1993). Motion perception between dissimilar gratings: a single chan nel theory. Vision Research, 33, 463-85) the motion strength of amplifier s andwich displays is proportional to the product m(o)m(e) for a wide range o f m(e). By setting m(e) to a large value, an amplifier sandwich stimulus wi th a very small value of mo can still produce visible motion. The amplifica tion factor is the ratio of two threshold modulation amplitudes: ordinary ( m) over cap (o=e) over amplified (m) over cap (o), (m) over cap (o=e)/(m) o ver cap (o). We find amplification factors of up to about 8 x. Light adapta tion and contrast gain control in early visual processing distort the repre sentations of visual stimuli so that inputs to subsequent perceptual proces ses contain undesired distortion products or 'impurities'. Motion amplifica tion is used to measure and thence to reduce these unwanted components in a stimulus to a small fraction of their threshold. Such stimuli are certifia bly pure in the sense that the residual impurity is less than a specified v alue. Six applications are considered: (1) removing (first-order) luminance contamination from moving (second-order) texture gratings; (2) removing lu minance contamination from moving chromatic gratings to produce pure isolum inant gratings; (3) removing distortion products in luminance-modulated (fi rst-order) gratings - by iterative application, all significant distortion products can be removed, (4) removing second-order texture contamination fr om third-order motion displays; (5) removing feature bias from third-order motion displays; (6) and the same general principles are applied to texture -slant discrimination in which x, y spatial coordinates replace the x, t mo tion coordinates. In all applicable domains, the amplification principle pr ovides a powerful assay method for the precise measurement of very weak sti muli, and thereby a means of producing visual displays of certifiable purit y. (C) 2001 Elsevier Science Ltd. All rights reserved.