1 / 21

Neural locus of color afterimages

Neural locus of color afterimages. Qasim Zaidi, Robert Ennis, Ding Cao, Barry Lee. Psychophysical Procedure. Historical Critical Experiments with Afterimages. Used by Al-Haytham to disprove the theory that visual rays emanated from the eye.

amelia
Download Presentation

Neural locus of color afterimages

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Neural locus of color afterimages Qasim Zaidi, Robert Ennis, Ding Cao, Barry Lee

  2. Psychophysical Procedure

  3. Historical Critical Experiments with Afterimages • Used by Al-Haytham to disprove the theory that visual rays emanated from the eye. • Used by Newton to first demonstrate inter-ocular interactions. • Used by Wheatstone to show that binocular vision does not require eye-movements.

  4. Proposed Neural Loci of Color Afterimages • Photoreceptors (Williams & MacLeod). • Post-receptoral (Loomis). • Cortical (Shimojo et al, Shevell et al). • Direct measurements of the neural locus have never been reported.

  5. Psychophysical Procedure

  6. Psychophysical Procedure

  7. Psychophysical Procedure • 3 cardinal directions at maximum monitor contrasts. • Eachstimulus was repeated 100 times divided into 10 sessions. The starting point of the clock was randomly jittered on each trial. • 5 color-normal observers

  8. Identity Points (Stimulus at 1/32Hz) (Means of 100 repeats per 5 observers) • Adaptation is lower for Δ(L+M+S) than Δ(L-M) despite 10 times greater • cone modulation by Δ(L+M+S), indicating post-receptoral adaptation.

  9. Advantages of the psychophysical method • The clock can be used for timing judgments without an attentional load. • Point of identity is much more definite than deciding when the afterimage has faded. • Linking Hypothesis: When the difference between the two halves becomes imperceptible, cell responses at some visual stage, should be back to baseline. • Can be used to make Class A measures of adaptation (Brindley,1970) as a function of spatial frequency, temporal frequency, etc.

  10. Recording from Retinal Ganglion Cells

  11. Physiological Stimulus

  12. Physiological Stimulus

  13. +M-Center Parvo-Ganglion Cell

  14. Ganglion Cell Adaptation Model • R(t) = Response at time t; R(0) = Baseline response • Q(t) = combination of cone inputs to ganglion cell • τ = time constant of adaptation • κ = subtractive constant • ν = adaptation strength constant (always 3) • Estimated parameters = R(0), κ, τ, ω,ν

  15. Ganglion Cell Adaptation Model • No Adaptation Fast Adaptation Slow Adaptation • Photoreceptor adaptation time constant = 0.01s (Smith, Pokorny, Lee, & Dacey, Vis. Research (2008)) • Stimulus value at response baseline should correspond to psychophysical nulled contrast. • “Rebound” response after the stimulus has returned to mean gray provides the afterimage signal to later stages. τ = 10000000s τ = 0.01s τ = 5s

  16. +S-Center Konio-Ganglion Cell

  17. ON-Center Magno-Ganglion Cell

  18. Virtues of Physiological Method • Measures adaptation state of neurons without using a probe that could disturb adaptation. • Provides a simple way to compare adaptation time constants of the neuron for different stimulus time-courses. • Estimated time constants were in the range of 4-10s.

  19. Response Maximum vs. Rebound Maximum

  20. Time-constants vs. Identity Points

  21. Conclusions • We identify a retinal locus for generation of color afterimage signals. • A subtractive adaptation model fits responses of Parvo-, Konio- and Magno- RGCs. • The slow time constants are consistent with post-receptoral adaptation following the combination of cone signals.

More Related