HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bauer, G. M. Articles by Nygaard, R. W. Search for Related Content PubMed PubMed Citation Articles by Bauer, G. M. Articles by Nygaard, R. W.

G. M. Bauer^*, T. E. Frumkes and R. W. Nygaard

Department of Psychology, Queens College of CUNY, Flushing, NY 11367, U.S.A.

1. The influence of rods on cone-mediated vision was assessed in eight human observers. To this end, increment threshold functions were obtained by determining thresholds of a cone-detected test flash (25 ms duration, 655 nm wave-length, 13' diameter) as a function of the illuminance of larger, 500 ms duration, rod-detected masking flashes. The type of photoreceptor influenced by each stimulus was carefully checked by means of a series of control procedures involving action spectra and selective rod adaptation.

2. When the rod mask was 512 nm in wave-length, 40' in diameter, and less than one scotopic td in illuminance, increment threshold functions show that [Formula: see text], where I_Cth is cone test threshold, I_R is rod mask illuminance, and D is a dark noise term similar to that used by Barlow (1956). Further increases in I_R have no additional influences on cone test threshold until threshold is influenced by the combined action of the mask on both rods and cones. If I_R is expressed in terms of scotopic flux rather than illuminance, the functional relationship obtained with all rod masks 40' diameter and 580 nm wave-length is identical.

3. Over the range of illuminance where a square-root relationship is obtained, probability of seeing functions show that a signal-to-noise mechanism limits the detectability of the cone test flash. These findings suggests a quantitative model in which cones produce a signal in a detector which is proportional to the illuminance of the cone test flash. Within a neural locus designated E (excitatory spatial summator), a response is produced which over at least a 40' diameter area, is proportional to the scotopic flux of the rod mask. E, however, feeds into a gain box, S, which saturates at illuminance levels at least 3 log₁₀ units less than usual estimates of rod saturation. Other than saturation, S behaves in a linear fashion.

4. As diameter increases beyond 60', rod masks of equal scotopic illuminance have progressively less influence on cone test threshold; rod masks > 2° have negligible influence on cone test threshold. We propose that I (inhibitory spatial summator), a neural locus which responds to scotopic flux provided over a very large area, attenuates the activity of E. The combined action of E and I is designated a rod channel. The response of cones and the rod channel summate at a detector. Within the detector, cone signals are distinguished from rod-related activity and intrinsic dark noise on the basis of signal-to-noise discriminations.

5. The neural substrate for this rod channel most probably involves the combined action of several neurones which synapse within the inner plexiform layer of the retina. The relationship of this rod channel to other perceptual phenomena is discussed.

To whom all correspondence should be addressed.

Present address: School of Optometry, University of California at Berkeley, Berkeley, CA 94720, U.S.A.