Michael A. Crognale

Photopigments and Color Vision in the Nocturnal Monkey, Aotus

The owl monkey (Aotus trivirgatus) is the only nocturnal monkey. The photopigments of Aotus and the relationship between these photopigments and visual discrimination were examined through (1) an analysis of the flicker photometric electroretinogram (ERG), (2) psychophysical tests of visual sensitivity and color vision, and (3) a search for the presence of the photopigment gene necessary for the production of a short-wavelength sensitive (SWS) photopigment. Both electrophysiological and behavioral measurements indicate that in addition to a rod photopigment the retina of this primate contains only one other photopigment type--a cone pigment having a spectral peak ca 543 nm. Earlier results that suggested these monkeys can make crude color discriminations are interpreted as probably resulting from the joint exploitation of signals from rods and cones. Although Aotus has no functional SWS photopigment, hybridization analysis shows that Aotus has a pigment gene that is highly homologous to the human SWS photopigment gene.

Visual evoked potentials in three-dimensional color space: Correlates of spatio-chromatic processing

Visual evoked potentials (VEPs) were measured for sinusoidal gratings with spatio-chromatic modulation defined in a three-dimensional color space. The spatio-chromatic modulation of the gratings can be decomposed into contributions from an achromatic luminance varying component, an isoluminant component which modulates only the activities of L cones and M cones, and an isoluminant component corresponding to modulation of only S-cone activity. The emphasis of this report is the nature of VEPs resulting from isoluminant spatio-chromatic modulation. The VEP response was characterized along a number of spatial, temporal, and chromatic stimulus dimensions: contrast, spatial frequency, chromaticity in the isoluminant plane, chrominance/luminance ratio, orientation, and temporal frequency. Isoluminant VEPs resulting from stimuli modulating L and M cones are compared with those from S-cone modulation. When appropriate spatiotemporal conditions are employed, both types produce robust VEPs; however, the S-pathway VEPs show considerably longer latencies than do those from LM-pathway activation. The VEP results are compared to psychophysical and single unit electrophysiological observations. VEP latencies exhibit the lowpass character of psychophysical chromatic contrast sensitivity functions but VEP amplitudes show bandpass tuning along both the S and LM axes. An oblique effect, i.e. shorter latencies for horizontal and vertical gratings than for diagonal, is observed in the isoluminant VEP. S-pathway VEPs are used to demonstrate an electophysiological correlate of transient tritanopia. Normative amplitude and latency data for VEPs from selectivity stimulated chromatic mechanisms provide a baseline for clinical electrodiagnostic applications.

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.

Development, maturation, and aging of chromatic visual pathways: VEP results

It has been argued that the development and aging of the different achromatic and chromatic visual pathways may proceed independently. We review here the evidence for such independent changes with particular emphasis on electrophysiological results. Changes in chromatic and achromatic visual processing throughout the life span were studied using visual evoked potentials (VEPs). VEPs were recorded in response to the presentation of patterns designed to preferentially stimulate achromatic and S-(L+M) and (L-M) chromatic mechanisms. Recordings were made in subjects aged 1 week to 90+ years. Longitudinal measurements were obtained from several infants and cross-sectional measurements were obtained from infants and older subjects. Responses to achromatic reversing patterns at low spatial frequencies appeared early and changed rapidly. Latencies of the achromatic reversal response decreased to mature values within the first 12-15 weeks of life. Responses to chromatic pattern onsets, however, appeared later (L-M: 4 weeks; S: 6-8 weeks) and changed continuously throughout the first year of life. Chromatic waveforms from 1 year to puberty appeared inverted relative to the adult waveform. The waveforms did not appear adultlike until about 12-14 years of age. The latencies of the major negative component of the adult response reached a minimum around 17-18 years of age. Throughout the remainder of the life span, VEP latencies steadily increased and amplitudes slightly decreased. Latencies of responses to chromatic pattern onsets increased more rapidly than latencies to moderate contrast achromatic pattern reversals.

Photopigments of dogs and foxes and their implications for canid vision

Electroretinogram (ERG) flicker photometry was used to examine the photopigment complements of representatives of four genera of Canid: domestic dog (Canis familiaris), Island gray fox (Urocyon littoralis), red fox (Vulpes vulpes), and Arctic fox (Alopex lagopus). These four genera share a common cone pigment complement; each has one cone pigment with peak sensitivity of about 555 nm and a second cone pigment with peak at 430-435 nm. These pigment measurements accord well with the conclusions of an earlier investigation of color vision in the dog, and this fact allows some predictions about color vision in the wild canids. An additional set of measurements place the peak of the dog rod pigment at about 508 nm.

Long-term maturation of visual pathways.

Previous research in adults has demonstrated the utility of the visual evoked potential (VEP) to measure the integrity of the chromatic and achromatic visual pathways. The VEP has also been shown to be a valuable indicator of maturation of these pathways in infants up to 1 year of age. The present manuscript reports changes in the visual pathways from 2 years to adulthood as measured by the spatio-chromatic VEP. The responses to achromatic reversal stimuli designed to preferentially activate the low spatial-frequency achromatic (luminance) pathways appear adult-like by 1 year of age. The responses to low spatial-frequency isoluminant onset stimuli designed to preferentially activate the chromatic pathway do not appear as they do in the adult until after 12-13 years of age. The shapes of the chromatic VEP waveforms shift from a positive-negative complex to a negative-positive complex. These changes can be modeled by a decrease in the latency of a large negative component between the ages of 1 year and adulthood. The results suggest that for low spatial-frequency stimuli, there are long-term changes in the development of the chromatic pathways that are not observed in the low spatial-frequency achromatic pathways. The changes in the chromatic VEP waveforms with age may be a physiological correlate of reported behavioral changes.

Development of the spatio-chromatic visual evoked potential (VEP): a longitudinal study

Most prior visual evoked potential (VEP) research on the development of color vision has employed pattern-reversing stimuli that are not optimal for producing chromatic responses. We measured infant VEPs using low spatial frequency, onset-offset stimuli, modulated along the three axes of a cone-based color space (Derrington et al. [J. Physiol 1984;357, 241-265.]). Three color-normal infants were tested in a longitudinal design over the first postnatal year. One red/green color-deficient infant was also tested at 197 days. We found that VEP responses to S-axis (tritan) stimuli have their initial onset later than responses to red/green (L-M) or achromatic stimuli, and that developmental changes in VEP waveforms are more complex and longer lasting for chromatic than for achromatic stimuli. Possible mechanisms underlying these changes are discussed.

Effective Rotations: Action Effects Determine the Interplay of Mental and Manual Rotations

The last decades have seen a growing interest in the impact of action on perception and other concurrent cognitive processes. One particularly interesting example is that manual rotation actions facilitate mental rotations in the same direction. The present study extends this research in two fundamental ways. First, Experiment 1 demonstrates that not only manual rotations facilitate mental rotations but that mental rotations also facilitate subsequent manual rotations. Second, Experiments 2 and 3 targeted the mechanisms underlying this interplay. Here, manual steering wheel rotations produced salient visual effects, namely the rotation of either a plane or a horizon in an aviation display. The rotation direction of these visual effects either did or did not correspond to the direction of the manual rotation itself. These experiments clearly demonstrate an impact of sensory action effects: Mental rotations facilitate manual rotations with visual effects of the same direction (as the mental rotation), irrespective of the direction of the manual rotation. These findings highlight the importance of effect anticipation in action planning. As such they support the contentions of ideomotor theory and shed new light on the cognitive source of the interplay between visual imagery and motor control.

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.

Cognitive and attentional changes with age: evidence from attentional blink deficits.

The attentional blink (AB) is a marked deficit in detecting a second target for up to 600 ms within a rapid serial visual presentation (RSVP). The phenomenon of the AB has typically been investigated using college students between 18 and 25 years of age. However, the AB has not been closely studied within a senior population. Past studies have found age-related attentional deficits using cued location, visual conjunction search, and divided-attention tasks, all spatial measures of attention; however, the physiological basis of these deficits is not fully understood. The role of cognitive slowing and reduced attentional resources was examined using the AB paradigm--a temporal measure of attention. Experiment 1 found an age-related deficit independent of lag for the single-task condition and a larger more prolonged deficit for dual-task conditions. Experiment 2, using similar methods to Experiment 1, incorporated a more rigorous cognitive screen. A similar deficit was found for the dual-task condition. However, single-task trials appeared to involuntarily capture attentional resources for the older population. Comparisons revealed a significant difference in the magnitude and the time course of the AB with age. Results are discussed in the context of cognitive slowing and reduced attentional resources.