Biomedical subjects

R E Walley

Publications and source records attributed to R E Walley.

10 recordsLinked to original sources

PubMed1989

Early interference in a priming task with brief masked targets.

Priming effects were examined in two experiments using either a pronunciation or lexical decision task. The prime, either a strong associate of the target, an unrelated word, or a neutral prime, was presented for 200 ms. After an SOA of 200, 400, or 800 ms, a masked target was presented for 33.3, 50, or 66.7 ms. Attention was manipulated by varying the probability that prime and target would be strongly associated. Both experiments showed significant interference in the low attention condition and at the 200-ms SOA, presumably before the onset of consciously directed processing. Two subsequent experiments using a short SOA and the low attention condition attempted to determine the conditions under which this interference will occur by varying the interstimulus interval, target duration, and the mask. It was found that interference occurred only when targets were brief and masked. These results are discussed in terms of a model involving lateral inhibition between nodes in semantic memory. It is suggested that when the target is brief and masked, the node in memory corresponding to the target is much less strongly activated and therefore more susceptible to the inhibitory effects of other activated nodes.

Attention↗

PubMed1988

Effect of low-intensity hippocampal stimulation on spatial versus working memory in rats.

A series of experiments was performed to investigate differing predictions from the spatial mapping hypothesis of hippocampal function proposed by O'Keefe and Nadel (1978) and the working memory hypothesis proposed more recently by Olton and his colleagues (Olton, Becker, & Handelmann, 1979). Each of two groups of rats was trained to use a different strategy to locate a submerged platform in a tank of opaque water. The MAP group used a spatial mapping strategy to reach a platform in a fixed location over trials; whereas the CUE group used a guidance strategy, which involved following a cue that signaled the location of a randomly placed platform on each trial. Following acquisition, one-half of each group was given low-level unilateral electrical stimulation of the dentate gyrus and immediately tested on the water maze task. The results of Experiment 1 showed that both the MAP and CUE groups were impaired by stimulation. However, it was observed that there was an inadvertent spatial element involved in the CUE task. When this element was eliminated in Experiment 3, the same CUE animals were not affected by a second series of stimulation trials, whereas the MAP animals continued to show impairment. These results are interpreted as strongly supporting the cognitive mapping hypothesis, while at the same time providing little support for the working memory hypothesis of hippocampal function.

Animals↗

PubMed1982

Specific and nonspecific changes in visual evoked potentials during eyelid conditioning in the rabbit (Oryctolagus cuniculus).

Eye blinks were conditioned to either the visual or nonvisual element of a compound conditioned stimulus. The visual element consisted of a series of electrical pulses to the optic chiasma, and the averaged evoked potentials (AEPs) produced by this stimulus were recorded in the dorsal lateral geniculate nucleus and the visual cortex. The initial surface positive component of the cortical AEP was enhanced only when the eye blinks were conditioned to the visual stimulus, an effect that cannot be attributed to nonspecific mechanisms. The "postsynaptic" component of the geniculate AEP was also enhanced, but this occurred regardless of whether the eye blinks were conditioned to the visual or nonvisual stimulus, an effect that appears to be entirely nonspecific. Data from recovery cycles indicate that this enhancement effect cannot be attributed to an inhibition of inhibitory interneurons in the lateral geniculate nucleus.

Animals↗

PubMed1977

Methylphenidate, amygdalectomy, and active avoidance performance in the rat.

Amygdalectomized and control rats were given 400 active avoidance training trials in a shuttle box. Control animals received 0, 4, 8, or 16 mg/kg of methylphenidate throughout acquisition. Amygdalectomized animals were given the first 200 trials without drug, followed by 200 trials with drug. The administration of methylphenidate produced an abrupt and large improvement in performance in the amygdalectomized animals. One month after acquisition under the drug, retraining without drug revealed a significant retention effect for the three amygdaloid-drug groups relative to the nondrug-amygdaloid group. These results indicate that although amygdalectomy impairs the performance of avoidance responses, it does not prevent the learning or retention of such responses. Since methylphenidate appears to act primarily on dopaminergic mechanisms, the possible influence of amygdalectomy on such mechanisms is discussed.

Amygdala↗

PubMed1974