Visual form perception from age 20 through 80 years.

PURPOSE: We measured performance on a battery of visual form perception tasks for adults sampled evenly from each decade of adult life from 20 to 80 years. METHODS: Measures were included that are considered to reflect processing at early through intermediate stages of the form processing pathways: collinear facilitation, center-surround contrast effects, global shape discrimination of contours of elements embedded in noise elements, and global shape discrimination in texture (Glass patterns). A total of 38 women and 20 men (mainly Caucasian, low refractive error) participated, aged between 20 and 82 years. RESULTS: With advancing age, contrast sensitivity decreased linearly (B = 0.009, t(56) = 8.14, P < 0.001), perceptual surround suppression of low contrast stimuli embedded in higher contrast surrounds increased (B = -0.006, t(56) = -3.32, P < 0.01), and coherence thresholds for detecting form in Glass patterns increased (B = 0.14, t(56) = 2.53, P = 0.02). Performance between tasks was not correlated. CONCLUSIONS: Several aspects of form perception alter gradually throughout the adult lifespan, namely context-dependent perception of contrast, and the extraction of global shape from texture. Our results suggested age-dependent differences under natural viewing conditions that are not predictable by standard clinical measures of visual function, and point to changes in neural function that are ongoing throughout adult life.

Shape perception is altered by normal aging.

PURPOSE: To compare the effects of aging on two shape-discrimination tasks: a closed shape task (radial frequency [RF] patterns) and a Glass pattern coherence task (discrimination of global shape signal from textured noise). We hypothesized that aging would impair the extraction of shape from texture more than the discrimination of closed shapes, consistent with evidence that aging impairs the ability to suppress irrelevant information when segmenting contours from noise. METHODS: Fourteen younger (19-38 years) and 14 older (62-72 years) adults participated. Contrast-detection thresholds were measured for the RF and Glass stimuli, and then shape-discrimination tasks were performed using stimuli of 5-fold each individual's contrast threshold. The threshold sinusoidal amplitude for the discrimination of an RF3 (triangular) versus an RF4 (square) was measured, in addition to the threshold signal coherence level for the discrimination of concentric from radial Glass patterns. RESULTS: Older adults had elevated shape-discrimination thresholds: RF: mean older = 27 second arc, younger = 18 second arc, t(26) = -3.14, P < 0.01; Glass patterns mean coherence: older = 29%, younger = 16%, t(26) = -5.67, P < 0.01. Relative to younger adult performance, the Z-scores for older adult performance on the Glass task were higher than the RF task (paired t-test; P < 0.05). CONCLUSIONS: Shape perception is not robust to the effects of aging. Greater deficits were manifest for the discrimination of shape from texture than for the discrimination of closed contours.

The effect of normal aging on closed contour shape discrimination.

Our experiments explore whether contour processing of closed shapes is altered by healthy aging. Contour processing was measured using a closed contour (circle or ellipse) constructed of Gabor elements. The contour was presented either on a blank background or embedded in noise (identical Gabor elements of random orientation). Twenty-one older (age range: 61-80 years) and 21 younger (age range: 22-38 years) adults participated in three experiments: 1) the number of Gabors comprising the contour was fixed (10, 12 or 15) and the threshold aspect ratio required to discriminate the shape (circle versus ellipse) was measured; 2) orientation jitter was added to the Gabor elements comprising the contour and shape aspect ratio discrimination thresholds were measured; and 3) the aspect ratio was fixed (three times the individual threshold aspect ratios) and the threshold number of elements required to determine the shape was measured. Older adults required a larger number of elements to discriminate the global contour shape (F(1, 41) = 15, p < 0.001), even when stimulus saliency was matched for contrast sensitivity and aspect ratio threshold. This finding is consistent with other recent work showing deteriorations in cortically mediated visual processing with age.

A role for omega-3 polyunsaturated fatty acid supplements in diabetic neuropathy.

PURPOSE: Diabetes results in an insulin-related disorder of lipid metabolism that reduces production of long-chain polyunsaturated fatty acids (PUFAs; e.g., docosahexanoic acid, DHA). This study considers the role that this lipid change has on retinal function. METHODS: From conception, rats (n = 56) were fed diets either balanced (n = 32) in PUFAs or deficient in omega-3 (n = 24). Half were assigned to control (n = 28) or streptozotocin (STZ: n = 28) treatment at 7 weeks of age. Key metabolic indices were assayed at 19 weeks, and retinal function was determined by electroretinogram (ERG) at 20 weeks. Retinal anatomy and lipid assays of 20-week-old animals were used to identify structural changes and tissue PUFA content. RESULTS: The systemic indices of diabetic rats were not affected by diet. Lipid composition of retinal membranes reflected the dietary manipulation, and diabetes amplified some fatty acid changes consistent with reduced desaturase activity. Diabetes produced significant reduction in rod function (-33%) only in the absence of fish oil, whereas cone responses (-46%) and inner retinal oscillatory potentials (-47%) showed either no effect of diet or a partial diet effect with a significant diabetes effect. Anatomic analysis revealed no disorder in the retinal neurons, although changes in the Müller glia were noted in diabetes, regardless of diet. CONCLUSIONS: A diet balanced in long-chain PUFAs modifies retinal lipid membranes in diabetes and prevents rod dysfunction. Dietary modification was not found in the cone or glial response but a partial improvement was evident in the OPs, most likely secondary to the larger photoreceptor output.