Academic journal article Canadian Journal of Experimental Psychology

The Age Deficit on Photopic Counterphase Flicker: Contrast, Spatial Frequency, and Luminance Effects

Academic journal article Canadian Journal of Experimental Psychology

The Age Deficit on Photopic Counterphase Flicker: Contrast, Spatial Frequency, and Luminance Effects

Article excerpt

Abstract This study evaluated the contribution of reduced contrast sensitivity and retinal illuminance to the age-related deficit on the temporal resolution of suprathreshold spatial stimuli. The discrimination of counterphase flicker was measured in optimally refracted young and elderly observers for sinusoidal gratings of three spatial frequencies (1, 4, and 8 cycles per degree) at three contrast levels (0.11, 0.33, and 0.66). Age deficits in flicker discrimination at the two higher contrast levels and at the two lower spatial frequencies were unrelated to observer contrast sensitivity. Flicker discrimination of young observers who carried out the task through .5 ND filters to simulate a two-thirds reduction of retinal illuminance in the older eye, was similar to that of the elderly observers. An age-related reduction in retinal luminance appears to be a major determinant of the age-related spatiotemporal deficit at suprathreshold contrast levels, although neural factors may also be involved.

Considerable evidence indicates that the senescent visual system is compromised in its ability to track temporal change and to resolve spatial detail in temporally modulated target stimuli (e.g., Kline, 1991; Kline & Scialfa, 1996; Owsley & Sloane, 1990; Spear, 1993). Although optical and sensorineural factors both appear to contribute to this loss, there is little consensus regarding their relative importance. Nor is it clear if the factors that limit spatiotemporal resolution at threshold contrast levels are the same as those that do so for suprathreshold stimuli. The goals of this study were to 1. determine the effects of target contrast and spatial frequency as a function of observer age and contrast sensitivity on the discrimination of counterphase flicker in suprathreshold sinusoidal gratings, and 2. estimate the contribution of reduced retinal illuminance to agerelated spatiotemporal deficits by comparing the thresholds of old observers at high luminance with those of young observers at high and low target luminance.

Studies of the spatial contrast sensitivity function (CSF) have typically reported a relative sparing of sensitivity (the reciprocal of contrast threshold) at low spatial frequencies (i.e., 1 c/deg and below) and an increasing age deficit at intermediate and high spatial frequencies (i.e., 2 c/deg and higher) (e.g., Burton, Owsley, & Sloane, 1993; Derefeldt, Lennerstrand, & Lundh, 1979; Elliott, 1987; Elliott & Whitaker, 1992; Elliott, Whitaker, & MacVeigh, 1990; Higgins, Jaffe, Caruso, & de Monasterio, 1988; Kline, Schieber, Abusamra, & Coyne, 1983; Owsley, Sekuler, & Siemsen, 1983; Scialfa, Tyrrell, Garvey, Deering, Leibowitz, & Goebel, 1988). Several studies have also observed a deficit at low spatial frequencies (e.g., Korth, Horn, Stork, & Jonas, 1989; Nameda, Kawara, & Ohzu, 1989; Ross, Clarke, & Bron, 1985; Sloane, Owsley, & Alvarez, 1988). Crassini, Brown, and Bowman (1988) have shown that the pattern of increasing age-related loss at higher spatial frequencies in the central retina also holds for the peripheral retina (10 degrees temporally). Although increased light scatter and attenuated retinal illuminance contribute to this loss (Guriao, Gonzalez, Redondo, Geraghty, Norrby, & Artal, 1999; Scialfa, Kline, & Wood, 2002), studies that have systematically varied optical factors (e.g., Elliott et al., 1990; Sloane, Owsley, & Alvarez, 1988), manipulated visual noise (Bennett, Sekuler, & Ozin, 1999; Pardhan, Gilchrist, & Elliott, 1996), or bypassed age-related optical effects using laser interferometry (Burton et al., 1993; Elliott, 1987), indicate that sensorineural factors also play a role. A recent study by Schefrin, Tregear, Harvey, and Werner (1999) reached a similar conclusion regarding aging effects on the scotopic CSF for the nasal retinal field. Significant age deficits at and below 1.2 c/deg were attributed by Schefrin et al. …

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