Jay Neitz

Electroretinogram flicker photometry and its applications

The electroretinogram (ERG) has been a traditional tool for the measurement and the analysis of spectral sensitivity. With the appropriate choices of stimulus and measurement conditions, the ERG permits a noninvasive examination of photopigment complement and provides the means for studying the combination of spectral signals at various locations throughout the retina. There are a number of practical problems associated with making spectral measurements with the ERG. One approach to minimizing these problems is to exploit the advantages of a flicker-photometric procedure. We summarize a method used to conduct ERG flicker photometry and illustrate a range of problems to which this technique can be successfully applied.

Color vision in the dog

The color vision of three domestic dogs was examined in a series of behavioral discrimination experiments. Measurements of increment-threshold spectral sensitivity functions and direct tests of color matching indicate that the dog retina contains two classes of cone photopigment. These two pigments are computed to have spectral peaks of about 429 nm and 555 nm. The results of the color vision tests are all consistent with the conclusion that dogs have dichromatic color vision.

Polymorphism in normal human color vision and its mechanism

Earlier we reported that Rayleigh matches made by males with normal color vision fall into distinct groups, and proposed that this behavior reflects an X-chromosome linked polymorphism in the spectral positioning of cone pigments (Neitz & Jacobs, 1986). In the present experiments two different color matches were obtained from each of 60 color normal males. Comparisons of the data from these two matches allowed variations in color matching that are produced by individual differences in the spectral positioning of middle and long wavelength cone pigments to be distinguished from color vision variations caused by other factors. Considered together with findings from molecular biology and spectral measurements of individual cone pigments, these results suggest that among color normal humans: (1) there are discrete variations in both middle and long wavelength cone pigments, and (2) most individuals have more than three different cone pigment types.

Color vision polymorphism and its photopigment basis in a callitrichid monkey (Saguinus fuscicollis)

The color vision of five saddle-backed tamarins (Saguinus fuscicollis) was studied. Behavioral tests of color discrimination and spectral sensitivity indicate that this species has a color vision polymorphism. Individual monkeys have either dichromatic or trichromatic color vision. Measurements of the spectral sensitivity of cones on this species were made on nine animals with the technique of electroretinogram (ERG) flicker photometry. Both the electrophysiological and the behavioral results suggest that there are four classes of cone pigment in this species. In addition to a short wavelength sensitive cone, apparently common to all tamarins, there are three classes of middle to long wavelength cone (lambda max = 545, 557 and 562 nm). Individual animals have either one or two of the latter types. The color vision variation in this species differs for males and females.

Electroretinogram measurements of cone spectral sensitivity in dichromatic monkeys

The corneal electroretinogram (ERG) was used to investigate the spectral sensitivities of cones in 12 dichromatic squirrel monkeys (Saimiri sciureus) whose color-vision capacities were established in behavioral tests. Three different varieties of dichromacy were represented among these animals. A flicker-photometric procedure was used in which the ERG response to a rapidly flickering monochromatic test light was compared with the response elicited by a similarly flickering reference light. The spectral-sensitivity functions obtained by the use of this technique are similar to previous estimates of cone spectral sensitivity in dichromatic squirrel monkeys derived from direct microspectrophotometric measurements.

Reexamination of Spectral Mechanisms in the Rat (Rattus norvegicus)

The spectral mechanisms of the rat were studied in electrophysiological and behavioral experiments. The photopic electroretinogram (ERG) was recorded (a) to rapidly flickering lights, (b) during the cone phase of dark adaptation, and (c) with a flicker photometric procedure. Each procedure indicated the presence of a single cone mechanism having a lambda max of about 510 nm. Increment-threshold spectral sensitivity functions measured in a behavioral test situation yielded the same conclusion. A behavioral experiment failed to produce any evidence for the presence of color vision in this rodent. The consistent conclusion from both behavioral and electrophysiological experiments is that the rat retina contains only a single photopic spectral mechanism.

Polymorphism of the middle wavelength cone in two species of south american monkey: Cebus apella and callicebus moloch

The spectral sensitivity of the middle wavelength cone was measured in two species of South American monkey, Cebus apella and Callicebus moloch, using electroretinogram (ERG) flicker photometry. Both of these species were found to have a polymorphism of the middle wavelength cone. Eight male Cebus monkeys each had only a single type of middle wavelength cone having lambda max values of either 550 or 562 nm. Eight Callicebus monkeys (7 male, 1 female) showed a similar polymorphism of the middle wavelength cone (lambda max = 549 or 561 nm). A single female of this latter species had two types of middle wavelength cone. The cone polymorphisms of these species appear very similar to that previously described for the squirrel monkey (Saimiri sciureus).

Spectral mechanisms and color vision in the tree shrew (Tupaia belangeri).

The retina of the tree shrew (Tupaia belangeri) is heavily cone dominated, rods comprising less than 4% of the total photoreceptors. Spectral mechanisms and color vision were investigated in this species in both behavioral and electrophysiological experiments. In confirmation of an earlier investigation, the tree shrew was found to have a clear spectral neutral point (at ca 505 nm) and is thus a dichromat. Spectral sensitivity functions determined in an increment threshold discrimination task show two clear peaks (at ca 440 and 550-560 nm) with an intermediate region of lowered sensitivity centered at about 500 nm. Spectral sensitivity of the two cone types in this animal were determined using ERG flicker photometry. One of these cone classes has a peak at 556 nm; the other has a 444 nm peak.

Color vision in squirrel monkeys: Sex-related differences suggest the mode of inheritance

Behavioral tests of vision in squirrel monkeys (Saimiri sciureus) reveal that there are widespread individual variations in color vision in this species. The variation has a sex-related component: whereas both trichromatic and dichromatic color vision occurs among female monkeys, males appear exclusively dichromatic. This finding suggests that, unlike humans, squirrel monkeys have only a single photopigment locus on the X chromosome.

Spectral sensitivity of ground squirrel cones measured with ERG flicker photometry

SummaryGround squirrels have dichromatic color vision. The spectral sensitivities of the two classes of cones found in the retinas of two species of ground squirrel were measured using ERG flicker photometry. The spectral sensitivity curves for these cone classes were closely fit by curves from wavelength-dependent visual pigment nomograms. One cone type had an average peak sensitivity of 518.9 nm (California ground squirrels,Spermophilus beecheyi) or 517.0 nm (thirteen-lined ground squirrels,Spermophilus tridecemlineatus). The second type of cone found in these ground squirrels had an average peak sensitivity of 436.7 nm. An examination of the variation in spectral sensitivity among individual animals suggests that the sensitivity peaks for the middle-wavelength cone cover a range of not greater than 4 nm.