Metacontrast and brightness discrimination

An attempt was made to obtain U-shaped masking functions in two metacontrast experiments. Trained Ss judged whether a square test stimulus (TS) was bright or dim. The TS was presented alone or in conjunction with an adjacent pair of square masking stimuli (MS) whose energy equaled the bright TS. The stimulus onset asynchronies (SOA) rangedfrom 0 to 125 msec. The task minimized the role of apparent movement cues as a reliable basis for judgrnent. Similar studies have employed TS plus MS vs MS alone as the alternatives, allowing apparent movement to be a cue. Brightness accuracy was a U-shaped function of SOA. This finding is consistent with neural-net models (Weisstein, 1968). However, analysis of Ss’ response bias suggested an alternative explanation involving the MS as a comparison stimulus at short SOA. It was concluded that U-shaped masking functions are also consistent with theories based upon independent component processes, e.g., Schurman and Eriksen (1970) and Uttal (1970).     

Effect of apomorphine on retention of a brightness discrimination in dopamine supersensitive rats

Apomorphine is known to improve the retention performance of a brightness discrimination task after post-training intrahippocampal application to rats. The present study shows that the retention performance of dopamine supersensitive rats was improved by a low dose of apomorphine which was still ineffective in control animals. Dopamine supersensitivity by itself had no effect on acquisition and retention parameters of brightness discrimination. The result further supports the assumption that dopamine receptors in rat hippocampus can modulate the formation of memory.     

Novel popout and familiar popout in a brightness discrimination task

A single novel word among several familiarized words may be localized more effectively than the familiarized words (novel popout). Early demonstrations of novel popout attributed the effect to the capture of attentional resources by novel stimuli. Christie and Klein (1995, 1996) argued that differential recollection of novel versus familiar words could alternatively account for the popout effect. In the present experiments, participants judged which of four locations contained a physically brighter word. A bright novel word was localized significantly better than a bright familiar word in one-novel/three-familiar arrays, inconsistent with a retrievability account of novel popout. However, a bright familiar word was also localized better than a bright novel word in three-novel/one-familiar arrays, inconsistent with the mismatch theory proposed by Johnston and Hawley (1994). The results suggest that familiarity and novelty provide a perceptual segregation of the odd item; superior brightness discrimination at that location may be due either to attentional capture or to locational ambiguity within the larger group.     

Spatial behaviour of normal and septal rats on alternate route maze problems

The behaviour of normal rats and rats with lesions of the septum was compared on a variety of alternate route variations of the three-table problem. In all variations of the task, septal rats were impaired on test trial performance when they displayed stereotypic body turn responses and demonstrated a strong preference for the most direct route between tables both during exploration and testing in all conditions. Normal rats displayed a similar route choice tendency in the simplest situations but shifted route choice behaviour in the most complex configuration, when they chose the inner, but longer, path. The use of the inner path may have allowed delayed-choice, single-point reference orientation, or reduction in the number of available alternatives. It is concluded that normal rats form a cognitive representation that allows them to identify environmental factors likely to facilitate solution, whereas septal rats rely on “taxon”-type strategies that can combine guidances and orientational responses.     

A diffusion model analysis of the effects of aging on brightness discrimination

The effects of aging on decision time were examined in a brightness discrimination experiment with young and older subjects (ages, 60-75 years). Results showed that older subjects were slightly slower than young subjects but just as accurate. Ratcliff's (1978) diffusion model was fit to the data, and it provided a good account of response times, their distributions, and response accuracy. There was a 50-msec slowing of the nondecision components of response time for older subjects relative to young subjects, but response criteria settings and rates of accumulation of evidence from stimuli were roughly equal for the two groups. These results are contrasted with those obtained from letter discrimination and signal-detection-like tasks.     

Stimulus displays which yield rapid learning of two-choice discrimination problems by rats

Stimulus displays yielding rapid learning of two-choice discrimination problems by rats were investigated. The results showed that rats learned step-through discriminations as haptic rather than as visual problems.