Analyses of human object recognition abilities led to the hypothesis that 2 kinds of spatial relation representations are used in human vision. Evidence for the distinction between abstract categorical spatial relation representations and specific coordinate spatial relation representations was provided in 4 experiments. These results indicate that Ss make categorical judgments--on/off, left/right, and above/below--faster when stimuli are initially presented to the left cerebral hemisphere, whereas they make evaluations of distance--in relation to 2 mm, 3 mm, or 1 in. (2.54 cm)--faster when stimuli are initially presented to the right cerebral hemisphere. In addition, there was evidence that categorical representations developed with practice.

In 2 experiments, we evaluated the ability of amnesic patients to exhibit long-lasting perceptual priming after a single exposure to pictures. Ss named pictures as quickly as possible on a single occasion, and later named the same pictures mixed with new pictures. In Experiment 1, amnesic patients exhibited fully intact priming effects lasting at least 7 days. In Experiment 2, the priming effect for both groups was shown to depend on both highly specific visual information and on less visual, more conceptual information. In contrast, recognition memory was severely impaired in the patients, as assessed by both accuracy and response time. The results provide the first report of a long-lasting priming effect in amnesic patients, based on a single encounter, which occurs as strongly in the patients as in normal Ss. Together with other recent findings, the results suggest that long-lasting priming and recognition memory depend on separate brain systems.

Short-term memory was assessed in two groups of amnesic patients. Six patients had confirmed or suspected damage to the hippocampal formation, and six patients had diencephalic damage as a result of alcoholic Korsakoff's syndrome. Verbal short-term memory was evaluated with seven separate administrations of the standard digit span test in order to obtain a precise measure of short-term memory. Nonverbal short-term memory was evaluated with four tests that assessed apprehension, retention, and the ability to manipulate nonverbal material-all within the span of immediate memory. One of these four tests assessed short-term memory for spatial location.Patients with damage to the hippocampal formation had a digit span equivalent to that of control subjects and also performed normally on the four tests of nonverbal short-term memory. The patients with Korsakoff s syndrome had a marginally low digit span and performed poorly on three of the four nonverbal tasks, a finding consistent with the deficits in attention and visuospatial processing previously described for this patient group. These deficits are likely due to the frontal lobe atrophy typically associated with Korsakoff s syndrome, rather than to diencephalic damage. The results support the view that short-term (immediate) memory, including short-term spatial memory, is independent of the hippocampus.

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A fonn of long-lasting repetition priming has been demonstrated by faster naming of pictirres repeated from a prior exposirre than new pictures. This facilitation is independent of explicit tneniov in both nonnal srrbjects (Mitcliell & Brown, 1988) and amtiesic patients (Cave & Sqdre, 1992). Using pictirre naniing. the cirrfent stirdy demonstrated that priming coirld be detected with delays of behveen 6 and 48 weeks behveeit the initial exposirre and the pritiiing test. Recognition riieniory was also above chance at these delay, birr perforinaiice on the two tars appeared independent. These resrrlts show that a single stiiiirrliis exposure can have wry long-lasting effects. Accounts of repetition priinirig as a fonn of iniplicit mernory will have to accornniodate long-lasting changes in sriniirlirs processing based on a single exposirre.Repetition priming (RP; facilitation in stimulus identification due to prior exposure) and other performance modifications have been important in understanding the organization of memory. RP is particularly interesting because it can be independent of explicit memory for stimuli (eg.. Schacter, 1987) and can occur on the basis of a single stimulus exposure.How long after a stimulus exposure can it influence later performance? In several early studies, priming effects disappeared within 2 hr after one or two exposures to words (Diamond &