Effect of laser eye protection devices on color perception.

Laser eye protection (LEP) devices may alter how colors are perceived in visual displays. This study investigates changes in color perception experienced by color-normal observers while wearing LEPs. Color perception with and without LEPs was measured using clinical color tests: City University Color Assessment and Diagnosis, Konan Medical ColorDx CCT-HD, and Farnsworth-Munsell 100-Hue. All LEPs induced a shift in color perception. The level of change in color perception significantly varied across LEPs. Consideration should be made when designing color displays where LEP devices are worn.

Increased surround modulation of perceived contrast in the elderly.

PURPOSE: The appearance of a stimulus depends on its background, with high-contrast backgrounds resulting in lower perceived contrast. Increased perceptual surround suppression effects have been reported in the elderly. Our experiments tested whether enhanced surround suppression in the elderly arises because of age-dependent differences in brightness induction mechanisms that are sensitive to phase information at the border of the central stimulus. METHODS: Fifteen younger (18 to 33 years) and 18 older (61 to 84 years) adults participated. Using a method of constant stimuli, perceived contrast was measured for a sine wave grating with and without an annular surround. Annuli were either in-phase with the central grating (suppresses the perceived central contrast) or out-of-phase (typically enhances perceived central contrast). The experiment was repeated using stimuli where the contrast was reduced for younger observers to approximately match the effective contrast available to older adults. RESULTS: With the surround present, the older group matched the contrast of the central target to an average lower contrast than younger adults [F(1,31) = 17.4, p < 0.001]. The magnitude of contrast suppression differences between older and younger observers was invariant of annulus grating phase [F(1,31) = 0.036, p = 0.85] and was of similar magnitude when the stimuli were approximately matched between groups for differences in contrast detection [F(1,31) = 0.06, p = 0.81]. CONCLUSIONS: Normal ageing increases perceived contrast surround suppression, irrespective of information at the stimulus border between center and surround. Conditions that result in perceived contrast enhancement on average in younger adults result in contrast suppression in the elderly. Our findings suggest that age-related differences are likely in the appearance of objects in natural environments where background contrast varies.

Aging alters surround modulation of perceived contrast.

It is well established that many visual functions deteriorate with age. Perhaps counter-intuitively, a recent study revealed that older people actually require less time to discriminate the direction of motion of large, high contrast moving stimuli than young adults (L. R. Betts, C. P. Taylor, A. B. Sekuler, & P. J. Bennett, 2005). L. R. Betts et al. (2005) proposed their finding as evidence for a reduction of cortical inhibitory function within the aging visual system. There is some neurophysiological support for this suggestion, as broadening of visual cortical neural tuning consistent with reduced inhibitory function has been observed in older animals. Here we explore the perceptual consequences of center-surround suppression within the healthy aging human visual system and report data from a center-surround contrast discrimination task (the Chubb contrast illusion). We predicted that older observers would demonstrate less center-surround suppression than younger subjects (consistent with reduced inhibition). Our data does not support this prediction as perceived contrast was altered more by surround modulation in the older than younger group (t(33) = 2.53, p = 0.02). A possible explanation for our findings is a decrease in perceptual brightness induction in the elderly group. Brightness induction relies on neural synchronization which might be disrupted by aging.

Contrast and stimulus duration dependence of perceptual surround suppression in older adults.

Most natural visual tasks involve the extraction of visual features from suprathreshold contrast backgrounds, hence an understanding of how ageing impacts on contrast mechanisms is essential to understand elderly visual function. Previous studies have revealed increased perceptual surround suppression of contrast in older adults. We aimed to determine whether such age-related effects depend on the centre or surround stimulus contrast as the neurophysiological mechanisms underpinning contrast-contrast suppression depend on such contrast relationships. We also measured surround suppression of contrast for longer duration and shorter duration stimuli to explore for effects of surround adaptation Fifteen younger and 15 older adults performed a centre-surround contrast discrimination task for a variety of centre-surround contrast combinations (20%, 40% and 80% contrast). Stimulus duration was 500ms. The 40% centre, 80% surround condition was also presented for 100ms duration. Relative to younger adults, perceptual surround suppression was increased for the older group for low, but clearly suprathreshold, central contrasts (20% contrast), whilst both groups performed similarly for stimuli with high centre contrasts. Data was best fit by a model with both increased inhibitory and excitatory weightings in the older group. Reduced stimulus duration increased perceptual surround suppression for both groups consistent with reduced adaptation to the surround, and did not explain the difference in suppression magnitude between groups. Understanding the stimulus parameters that elicit increased surround suppression in older adults is key to directing future work exploring underlying neural substrates, in addition to potentially being useful for predicting performance on more complicated natural visual tasks such as object and scene perception.

Age related changes to perceptual surround suppression of moving stimuli.

Perceptual analogues of centre-surround suppression have been applied as indirect measures of cortical inhibitory function in several clinical disorders. Two tasks have been used: a centre-surround contrast perception task and a motion direction discrimination task, where the stimulus size and contrast is varied to measure surround suppression effects. The tasks are markedly different, yet previous literature implies that both measures indirectly assess inhibitory function and that results will be complementary. This is not the case for age-related effects on surround suppression, however, as previous reports using the different measures are conflicting. Here we use a low-spatial frequency, drifting grating version of the centre-surround contrast perception task, and compare results to those obtained with the motion direction task in a single group of older observers. Older adults demonstrate significantly increased perceptual surround suppression of contrast for drifting, high contrast stimuli. Using the motion discrimination task, older observers showed similar amounts of surround suppression for the largest stimulus. This study confirms that visual surround suppression is altered by ageing. The complexity of neuronal systems involved in centre-surround interactions makes it unlikely that a single perceptual task will be sufficient to describe the effects of clinical disorders on surround suppression.