Visual discrimination

Rats exposed to 1,000 ppm TCE for 3 days had disturbed sleep cycles (Arito et al. 1993). Rats exposed to 1,000 ppm for 18 weeks showed increased latency in visual discrimination tasks (Kulig 1987). Sleep apnea has been observed in humans exposed to organic solvents (Edling et al. 1993 Monstad et al. 1987, 1992 Wise et al. 1983). Cardiac arrhythmia has been observed in humans exposed to trichloroethylene vapor (Dhuneretal. 1957 Hewer 1943 Milby 1968 Pembleton 1974 Thiersten et al. 1960). 

At its most fundamental level, the circadian cycle rests on the influence of so-called clock genes . These genes have been studied most extensively in insects but they have also been found in humans. Their protein products enter the cell nucleus and regulate their own transcription. This feedback process is linked to exposure to light and so it is not surprising that visual inputs are important for maintenance of circadian rhythms. However, it is not the reception of specific visual information, transmitted in the optic nerve to the lateral geniculate nucleus (LGN) and visual cortex (i.e. visual discrimination), that is responsible for the rhythm but the more simple, almost subconscious, reception of light. 

Lambs exposed to low levels (350 pg Pb/L blood) Impaired visual discrimination and learning 17... 

Three male squirrel monkeys previously trained to perform visual discrimination or visual acuity threshold tests were exposed continuously for 90 d to PGDN at a concentration of 262 mg/m3 (approximately 37 ppm) (Jones et al. 1972). The animals were removed from the exposure chambers for a 2-h period once a week for the respective behavior tests. A fourth trained monkey exposed to filtered room air under the same conditions served as the control. The only sign during exposure was mydriasis (excessive dilatation of the pupil of the eye), which increased from slight to moderate. There were no changes in avoidance behavior in the monkeys as determined by the visual tests. 

Exposure of nonsmokers to 50 ppm for 6-8 hours results in carboxyhemoglobin levels of 8-10%. Several investigators have suggested that the results of behavioral tests such as time discrimination, visual vigilance, choice response tests, visual evoked responses, and visual discrimination threshold may be altered at levels of carboxyhemoglobin below 5%. ... 

In mice, the intravenous LD50 was greater than 25 mg/kg, and the MEDjq (median effective dose) was 0.1 mg/kg, for a safety margin greater than 250. In the dog, slight hypertension was seen at 0.1 and 1 mg/kg. In monkeys trained on a visual discrimination test, minimal behavioral effects were seen at 0.316 mg/kg, and moderate to marked effects at 1.0 mg/kg. 

Stickgold R, Whidbee D, Schirmer B, Patel V, Hobson JA. Visual discrimination task improvement a multi-step process occurring during sleep. J Cognit Neurosci 2000 12(2) 246-254. 

On a task of visual discrimination - the Karni-Sagi task, for example - individuals improve their performance without knowing how or why (as they learn the task) after sleep they then do better... 

McGonigle, B. (1967). Stimulus additivity and dominance in visual discrimination by rats. Journal of Comparative and Physiological Psychology, 64, 110-112. 

Evenden JL, Marston HM, Jones GH, Giardini V, Lenard L, Everitt BJ, Robbins TW (1989) Effects of excitotoxic lesions of the substantia innominata, ventral and dorsal globus pallidus on visual discrimination, acquisition, performance and reversal in the rat. Behav Brain Res 32 129-149. 

Several studies have tested visual function after exposure to carbon monoxide. To minimize variability, McFarland et al. (1944) studied brightness discrimination in a small group of well-trained subjects. The subjects reported decreases in visual sensitivity at approximately 4.5% COHb. Another study reported no adverse effects on visual discrimination or depth perception in subjects with 8% or 12% COHb (Ramsey 1973). Luria and McKay (1979) reported no decrement in night vision with COHb of 9%. Davies et al. (1981) reported that at 7% COHb there was no effect on visual function. The studies described above used various visual paradigms, which could account for the differences in results. 

Rapp PR (1990) Visual discrimination and reversal learning in the aged monkey (Macaca mulatta). Behav Neurosci 104 876-884... 

Roberts AC, Robbins TW, Everitt BJ, Jones GH, Sirkia TE, Wilkinson J, Page K (1990) The effects of excitotoxic lesions of the basal forebrain on the acquisition, retention and serial reversal of visual discriminations in marmosets. Neuroscience 34 311-329... 

Myhrer, T. (2000). Effects of selective perirhinal and postrhinal lesions on acquisition and retention of a visual discrimination task in rats. Neurobiol. Learn. Mem. 73 68-78. 

Visual discrimination was reduced by doses of 7-31 yg/kg. Tachycardia and decreased activity followed doses of about 130 yg/kg. Prostration and convulsions were produced by doses of 14-16 mg/kg ... 

In a similar task Involving visual discrimination and escape by monkeys, the sequence of effectiveness of the two numbered compounds was EA 3580 and EA 3443. It Is clear that none of Che screening tests with experimental animals had reproduced the sequence of potencies found In the human test. The author of the report suggested that groups of animals larger than the two of each species required for the screening tests might Increase the reliability of the results obtained with laboratory animals. 

Studies with human infants find that at even one or two days of age, they are able to perform detailed visual discriminations, and they show preferences for visually complex or novel stimuli. While this line of research cannot prove the ability is not learned, it does lend support to these abilities being present at birth in some form. 

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