Abstrset-The determination of the relative numbers of different cone types in the human retina is fundamental to our understanding of visual sensitivity and color vision; yet direct measurements which provide this basic information have not previously been made for ail cone types. Here we present a model which links the detection of a test light of small dimension to the number of cones contributing to detecfon of the light. We selectively isolated either the long-wavelength-sensitive (L) or the middle-wavelengthsensitive (M) cones, by choosing combinations of wavelengths of adapting backgrounds and tests to favor detection by the cone class of interest. Our model was applied to the detection functions measured for six color normal observers to obtain estimates of the relative numbers of L to M cones. Our estimates ranged between 1.46 and 2.36 for our observers with a mean value near two L cones for every M cone in human fovea centralis. ConesHuman fovea centralis Relative numbers of L to M cones ~RODU~ONThe determination of the relative numbers of different cone types in the retina is fundamental to our understanding of human visual sensitivity and color vision, and this information would be required for any quantitative models of human vision. Direct measurements which provide this basic information have not been previously made for all cone types. There continues to be a gratifying convergence of psychophysically derived evidence from humans ~Williams et al., 1981) and anatomically derived evidence from baboon (Marc and Sperling, 1977), macaque (deMonasterio et al., 1985), and human (Ahnelt et al., 1987) on the numerosity and distribution of the shortwavelength-sensitive (S) cones in the primate retina.In the cases of the long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones, there are no previous direct psychophysical measurements from which the relative numbers of L and M cones can be derived, and estimates based on various indirect means vary widely. To our knowledge, DeVries (1946DeVries ( , 1948 was the first to suggest that the individual variability in luminosity functions could be related to individual variability in the relative numbers of different cone types. Rushton and Baker (1964) subsequently reported that retinal densitometric measurements yielding the density of M and L cone pigments could be correlated to the flicker photometric matches between red and green lights made by their observers. Rushton and Baker's estimates, based on densitometric measurements, of the relative numbers of L to M cones in normal trichromatic observers spanned a wide range of three times more L as compared to M cones to one third as many L as compared to h4 cones. Another approach has been based on estimates deriving from curve fits required to make various sets of psychophysical data consistent one to another. Examples of this kind of analysis include Walraven's (1974) and Smith and Pokorny's (1975) estimates based on fits of the cone primaries to the luminosity function; Vos and Walraven's (1971)...

Electrophysiological recordings were made in 21 observers to investigate whether differences in signature components (P1, N1, selection negativity [SN]) would be revealed during perceptual reversals of three different multistable figures. Using a lattice of Necker cubes as a stimulus, J. Kornmeier and M. Bach (2004, 2005) reported differences in P1 amplitudes as well a broad reversal-related negativity occurring 200-400 ms poststimulus. The current study investigated whether these event-related potentials of Necker cube reversals represent general "perceptual switching" mechanisms and would, therefore, be common to other types of multistable figures. Three different types of multistable stimuli were utilized: a modified Rubin's face/vase, a modified Schröder's staircase, and a novel natural stimulus, Lemmo's cheetahs. Results revealed the broad reversal-related negativity for the face/vase and the reversible staircase but not for the cheetahs. This component is comparable to the SN in polarity, latency, and scalp topography. An effect of early visual spatial attention on figure reversals was suggested by an analysis of the occipital P1 and N1 components. The P1, N1, or both were enhanced for trials in which the observer reported perceptual reversals compared with trials in which no reversals were reported for the face/vase and reversible staircase stimuli. These results support a model of multistable perception in which changes in early spatial attention (indicated by P1 and N1 enhancement) modulate perceptual reversals (indicated by the reversal negativity or SN).

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Multistable perception occurs when a single physical stimulus leads to two or more distinct percepts that spontaneously switch (reverse). Previous ERP studies have reported reversal negativities and late positive components associated with perceptual reversals. The goal of the current study was to localize the neural generators of the reversal ERP components in order to evaluate their correspondence with previous fMRI results and to better understand their functional significance. A Necker-type stimulus was presented for brief intervals while subjects indicated their perceptions. Local auto-regressive average source analyses and dipole modeling indicated that sources for the reversal negativity were located in inferior occipital-temporal cortex. Generators of the late positive component were estimated to reside in inferior temporal and superior parietal regions. DescriptorsSensation/perception; EEG/ERP; Cognition Ambiguous figures are physically unchanging images that can be alternately perceived in two or more different ways. One of the best known is the Necker cube, which can be perceived as a three-dimensional (3D) cube facing either leftward or rightward. Such figures are experimentally useful for analyzing the neural basis of perceptual experience because sensory input remains fixed while distinct perceptual changes ("reversals") occur.Recordings of event-related potentials (ERPs) have identified two components associated with perceptual reversals, the "reversal negativity" (RN) and the "late positive component" (LPC; Basar-Eroglu, Struber, Stadler, Kruse, & Basar, 1993;Britz, Landis, & Michel, 2009; IsogluAlkac et al., 1998;Kornmeier & Bach, 2004Kornmeier, Ehm, Bigalke, & Bach, 2007;O'Donnell, Hendler, & Squires, 1988;Pitts, Gavin, & Nerger, 2008;Pitts, Nerger, & Davis, 2007;Struber, Basar-Eroglu,Miener, & Stadler, 2001). The RN component, which is maximal over parietal-occipital scalp regions, begins at ~170 ms after the stimulus, peaks at 250 ms, and persists until ~350 ms. This component can be isolated by presenting an ambiguous figure intermittently, time-locking ERP recordings to stimulus onset, and comparing trials with the same percept as on the previous trial (stable) to those with the alternate percept (reversal). The LPC, which has a central/parietal scalp distribution, begins at approximately 300 ms, peaks around 450 ms, and persists beyond 550 ms. The LPC was initially reported in studies that presented sustained ambiguous figures and time-locked recordings to subjects' motor Copyright © 2009 Society for Psychophysiological Research Address reprint requests to: Steven Hillyard, School of Medicine, Department of Neurosciences, University of California, San Diego, 9500 Gilman Drive, MC 0608, La Jolla, CA 92093-0608, USA. shillyard@ucsd.edu. NIH Public Access Author ManuscriptPsychophysiology. Author manuscript; available in PMC 2010 July 1. Published in final edited form as:Psychophysiology. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript responses indicatin...

Unique hue loci were measured for four observers in the fovea and at 20-deg temporal eccentricity as a function of test size. Eccentric measurements were made on the cone plateau following a rod bleach. The results indicate that unique yellow remains approximately invariant with respect to test size and retinal eccentricity, whereas unique blue and unique green shift to longer wavelengths with increasing test size. The locus of unique blue in the periphery reaches an asymptote at approximately the same wavelength as that from the foveal measurements, whereas unique green measured in the periphery is consistently at shorter wavelengths than in the fovea. In general, the data are best described by a model in which the short-wavelength-sensitive cone input to the two opponent-color channels decreases with decreasing test size and increasing retinal eccentricity.