Lateral eyes or lateralized? Hemiretinal and ocular dominance effects on visual field asymmetries for the lexical decision task.

The effects of hemiretinal stimulation and ocular dominance on a visual half-field lexical decision task were investigated. Twelve right-eyed and 12 left-eyed subjects made word/nonword decisions about stimuli presented in the left and right visual field under binocular, left-eye alone, and right-eye alone viewing conditions. Both accuracy (d') and response time measures were recorded. The nasal hemiretina advantage for response time and temporal hemiretina advantage for accuracy found for face recognition (Proudfoot, 1983, Brain and Cognition, 2, 25-31) were not present when lexical decisions were made. An overall right visual field advantage was present for both eye-dominance groups. The results support a hemispheric interpretation of visual field differences for the processing of words during lexical decision.

Temporal summation functions for detection of sine-wave gratings in young and older adults.

Temporal summation functions for 0.416 and 7.5 c/deg sinusoidal gratings were measured in young and old observers in order to test the hypothesis of a shift in sensitivity from "transient" to "sustained" channels in the aging visual system. Results failed to support the transient-shift hypothesis. Additional tests showed no age-related changes in temporal summation even within a single channel. When all observers were refracted for the test distance and matched for retinal illuminance, no age-related differences in contrast sensitivity were found.

Older observers have attenuated increment thresholds upon transient backgrounds.

Foveal increment thresholds were measured in young, middle-aged, and older observers. These thresholds, which involved the detection of a small test flash as a function of the intensity of a larger background adapting field (AF), were measured at the instant of onset of the AF (transient condition) and when the eye had been fully light adapted to the AF (steady-state condition). All stimuli were presented to the left eye in a free-viewing system through a 2 mm artificial pupil. For the steady-state condition for all age groups, the functions were similar, but for the transient condition, the slope for the older observers was significantly less steep than that for the younger observers. These findings are consistent with an hypothesis of a selective loss of transient (Y) channels in the aging visual system.

Lexical judgments after right- or left-hemisphere injury.

Patients with unilateral left- or right-hemisphere lesions were asked to make similarity judgments to visually presented words on the basis of rhyme, meaning or visual similarity. The left-hemisphere-injured group was significantly impaired, relative to controls, for all types of lexical judgments, with the greatest impairment in the rhyme condition. Patients with right-hemisphere injury were also impaired, but only when lexical judgments were based on meaning. The results are generally consistent with normal and split-brain lateralization findings, and provide evidence supportive of a right-hemisphere contribution to some aspects of lexical semantic processing.

Automatic and controlled semantic priming: accuracy, response bias, and aging.

Adult age differences in automatic and controlled semantic priming were investigated by varying the probability of valid primes in a lexical decision task. Tachistoscopic parafoveal stimulus presentation was used to assess age differences in accuracy and response bias as well as latency. Both age groups showed the expected findings of benefits without costs under automatic priming and benefits and costs under controlled priming. Errors for young adults were distributed equally among word and nonword stimuli, whereas older adults displayed a strong tendency to commit errors on nonword trials.