Anomalous trichromacy is a form of color vision deficiency characterized by the presence of three... more Anomalous trichromacy is a form of color vision deficiency characterized by the presence of three cone types, but with shifted spectral sensitivities for L or M cones, causing a red-green color deficiency. However, long-term adaptation to this impoverished opponent input may allow for a more normal color experience at the suprathreshold level ("compensation"). Recent experimental evidence points to the presence of compensation in some tasks. The current study used threshold detection, suprathreshold contrast matching, and a reaction-time task to compare contrast coding in normal and anomalous observers along the cardinal cone-opponent axes. Compared to color normals, anomals required more L-M contrast, but not S contrast, to detect stimuli and to match an achromatic reference stimulus. Reaction times were measured for several contrast levels along the two cone-opponent axes. Anomals had higher overall reaction times, but their reaction-time versus contrast functions could be matched to those of controls simply by scaling contrast by the detection thresholds. Anomalous participants were impaired relative to controls for L-M stimuli in all three tasks. However, the contrast losses were three times greater for thresholds and reaction times than for suprathreshold matches. These data provide evidence for compensation in anomalous trichromats, but highlight the role that the experimental task plays in revealing it.
Many ocular diseases are reported to produce a sensitivity loss for specific achromatic or chroma... more Many ocular diseases are reported to produce a sensitivity loss for specific achromatic or chromatic pathways, particularly short-wavelength-sensitive cone (S-cone) pathways. To study these losses we have measured VECPs using spatio-chromatic stimuli which vary along directions in the color space proposed by MacLeod & Boynton (1978) and augmented by Krauskopf et al. (1982). Such stimuli, by maintaining the same time-averaged luminance and chrominance, avoid the complications of chromatic adaptation while allowing selective activation of various pathways. We report how this technique can be used to analyze selective sensitivity loss in retinal disease. Specifically, we studied losses in a subject with a history of central serous choroidopathy. VECPs elicited from stimulation of the affected eye are compared with those elicited from the unaffected eye and with responses from normal subjects. For the affected eye we find that response amplitudes for 1 c/deg gratings modulated along the S axis are greatly reduced compared to those from the unaffected eye and for normals. No interocular response difference is observed for stimuli which vary along the L-M, L or M axes or for luminance modulated stimuli. Comparison of VECPs evoked by S axis modulation between different retinal regions of the affected eye reveals a regional loss. The results illustrate how these techniques can reveal selective losses in ocular disease.
Purpose: Changes in retinal photopigments represent a fundamental step in the evolution of visual... more Purpose: Changes in retinal photopigments represent a fundamental step in the evolution of visual systems, in that addition of new pigment types or alterations in the spectral absorption properties of existing pigments modify visual capacities and thus open new visual worlds. To provide a tool that would allow direct examination of the changes caused by the presence of novel photopigments, this study was designed to determine whether a gene encoding a human cone photopigment introduced into the mouse genome would be expressed in a cone-specific manner and would support phototransduction. Methods: Mice transgenic for the human long wavelength-sensitive (L) photopigment were generated by microinjection of fertilized mouse eggs. RNA expression in different tissues was monitored by reverse transcription-polymerase chain reaction analysis. Photopigment protein was localized in retinal cross sections and wholemounts by antibody staining. Light transduction of the cone photopigments was assessed by flicker photometric electroretinography (ERG). Results: The human transgene was expressed specifically in the mouse cones in quantities comparable to those of the mouse middle wavelength-sensitive (M) pigment gene. Immunocytochemical analysis showed that the human L pigment was abundantly synthesized in most mouse cones, was translocated to the outer segments, and caused no detectable cone degeneration. Electroretinographic spectral sensitivity analysis showed that the human L pigment was efficient in eliciting an electrical response. The degree of expression of the transgene in the two founders correlated well with the spectral responsivity of the ERG. Conclusions: The human L photopigment transduces light efficiently in mouse cones, implying that all protein domains necessary for efficient interaction with intracellular transport and signal transduction machineries in mouse cones have been conserved through evolution. The expression of the human L photopigment gene in both classes of cone of the mouse retina indicates that the transgene did not have the regulatory elements necessary for restricting its expression to mouse M cones or that such elements are not recognized in mouse UV-sensitive cones.
This chapter examines categorical colour perception and the nature of central processing of colou... more This chapter examines categorical colour perception and the nature of central processing of colour in a 33-year-old male with X-linked incomplete achromatopsia. Data from colour naming and categorization, colour contrast adaptation, and a battery of standard colour tests performed with and without a rod bleach, are presented. It is shown that despite colour deficiencies, the subject demonstrates consisted but shifted colour category and naming behaviour, while showing weak evidence for selectively tuned central chromatic mechanisms.
Anomalous trichromacy is a form of color vision deficiency characterized by the presence of three... more Anomalous trichromacy is a form of color vision deficiency characterized by the presence of three cone types, but with shifted spectral sensitivities for L or M cones, causing a red-green color deficiency. However, long-term adaptation to this impoverished opponent input may allow for a more normal color experience at the suprathreshold level ("compensation"). Recent experimental evidence points to the presence of compensation in some tasks. The current study used threshold detection, suprathreshold contrast matching, and a reaction-time task to compare contrast coding in normal and anomalous observers along the cardinal cone-opponent axes. Compared to color normals, anomals required more L-M contrast, but not S contrast, to detect stimuli and to match an achromatic reference stimulus. Reaction times were measured for several contrast levels along the two cone-opponent axes. Anomals had higher overall reaction times, but their reaction-time versus contrast functions could be matched to those of controls simply by scaling contrast by the detection thresholds. Anomalous participants were impaired relative to controls for L-M stimuli in all three tasks. However, the contrast losses were three times greater for thresholds and reaction times than for suprathreshold matches. These data provide evidence for compensation in anomalous trichromats, but highlight the role that the experimental task plays in revealing it.
Many ocular diseases are reported to produce a sensitivity loss for specific achromatic or chroma... more Many ocular diseases are reported to produce a sensitivity loss for specific achromatic or chromatic pathways, particularly short-wavelength-sensitive cone (S-cone) pathways. To study these losses we have measured VECPs using spatio-chromatic stimuli which vary along directions in the color space proposed by MacLeod & Boynton (1978) and augmented by Krauskopf et al. (1982). Such stimuli, by maintaining the same time-averaged luminance and chrominance, avoid the complications of chromatic adaptation while allowing selective activation of various pathways. We report how this technique can be used to analyze selective sensitivity loss in retinal disease. Specifically, we studied losses in a subject with a history of central serous choroidopathy. VECPs elicited from stimulation of the affected eye are compared with those elicited from the unaffected eye and with responses from normal subjects. For the affected eye we find that response amplitudes for 1 c/deg gratings modulated along the S axis are greatly reduced compared to those from the unaffected eye and for normals. No interocular response difference is observed for stimuli which vary along the L-M, L or M axes or for luminance modulated stimuli. Comparison of VECPs evoked by S axis modulation between different retinal regions of the affected eye reveals a regional loss. The results illustrate how these techniques can reveal selective losses in ocular disease.
Purpose: Changes in retinal photopigments represent a fundamental step in the evolution of visual... more Purpose: Changes in retinal photopigments represent a fundamental step in the evolution of visual systems, in that addition of new pigment types or alterations in the spectral absorption properties of existing pigments modify visual capacities and thus open new visual worlds. To provide a tool that would allow direct examination of the changes caused by the presence of novel photopigments, this study was designed to determine whether a gene encoding a human cone photopigment introduced into the mouse genome would be expressed in a cone-specific manner and would support phototransduction. Methods: Mice transgenic for the human long wavelength-sensitive (L) photopigment were generated by microinjection of fertilized mouse eggs. RNA expression in different tissues was monitored by reverse transcription-polymerase chain reaction analysis. Photopigment protein was localized in retinal cross sections and wholemounts by antibody staining. Light transduction of the cone photopigments was assessed by flicker photometric electroretinography (ERG). Results: The human transgene was expressed specifically in the mouse cones in quantities comparable to those of the mouse middle wavelength-sensitive (M) pigment gene. Immunocytochemical analysis showed that the human L pigment was abundantly synthesized in most mouse cones, was translocated to the outer segments, and caused no detectable cone degeneration. Electroretinographic spectral sensitivity analysis showed that the human L pigment was efficient in eliciting an electrical response. The degree of expression of the transgene in the two founders correlated well with the spectral responsivity of the ERG. Conclusions: The human L photopigment transduces light efficiently in mouse cones, implying that all protein domains necessary for efficient interaction with intracellular transport and signal transduction machineries in mouse cones have been conserved through evolution. The expression of the human L photopigment gene in both classes of cone of the mouse retina indicates that the transgene did not have the regulatory elements necessary for restricting its expression to mouse M cones or that such elements are not recognized in mouse UV-sensitive cones.
This chapter examines categorical colour perception and the nature of central processing of colou... more This chapter examines categorical colour perception and the nature of central processing of colour in a 33-year-old male with X-linked incomplete achromatopsia. Data from colour naming and categorization, colour contrast adaptation, and a battery of standard colour tests performed with and without a rod bleach, are presented. It is shown that despite colour deficiencies, the subject demonstrates consisted but shifted colour category and naming behaviour, while showing weak evidence for selectively tuned central chromatic mechanisms.
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Papers by Michael Crognale