• Corpus ID: 16580204

THE APPLIED VISION ASSOCIATION IS A REGISTERED CHARITY NO: 1049146 COMMITTEE OF MANAGEMENT Chairman: Vice chair: Treasurer: Bulletin of the AVA: Publicity Officer:

@inproceedings{Moorhead1997THEAV,
  title={THE APPLIED VISION ASSOCIATION IS A REGISTERED CHARITY NO: 1049146 COMMITTEE OF MANAGEMENT Chairman: Vice chair: Treasurer: Bulletin of the AVA: Publicity Officer:},
  author={Ian R. Moorhead},
  year={1997}
}

• I. Moorhead
• Published 1997

presented at ECVP Motion contrast: a new metric for direction discrimination N.E. Scott-Samuel* and M.A Georgeson School of Psychology, University of Birmingham, Birmingham, B15 2TT, U.K. (*current address: Department of Psychology, Royal Holloway, Egham, TW20 OEX, U.K.) Email: [e-mail], [e-mail] The Adelson-Bergen energy model (1985 Journal of the Optical Society of America A 2 284-299) is a standard framework for understanding 1storder motion processing. Its output, the oppenent energy for a given output is calculated by subtracting one directional energy measure (L) from its opposite (R), and its sign indicates the direction of the motion of the input. Our observers viewed a dynamic sequence of gratings (1 c/deg) equivalent to the sum of the two grating movings in the opposite directions with different contrasts, and had to report the dominant direction of motion. The ratio of contrasts was varied across trails. We found the opponent energy was a very poor predictor of direction discrimination performance. Heeger (1992 Visual Neuroscience 9, 181-197) has suggested the divisive inhibition amongst striate cells requires a contrast gain control in the energy model. A new metric can be formulated in the spirit of Heeger’s model by normalising the opponent energy (L-R) with a flicker energy, the sum of the directional motion energies (L + R). This new measure, motion contrast (L-R)/(L+R), was found to be a good predictor of direction discrimination performance over a wide range of contrast levels, but opponent energy was not. Discrimination thresholds expressed as motion contrast were around 0.5 for the sampled drifting gratings used in our experiments, corresponding to an energy ratio (L:R or R:L) of 3:1 at discrimination threshold. Such high values suggest that the outputs of motion energy filters are very noisy (variable over space and time) or that the use of them is inefficient.