Contributions of the dorsal hippocampus and the dorsal subiculum to processing of idiothetic information and spatial memory

It is well established that the dorsal hippocampal formation is crucial for spatial memory in rats. However, little is known about the distinct functions of the dorsal hippocampus and the dorsal subiculum. To examine the role of the dorsal hippocampus and the dorsal subiculum, Long-Evans rats with excitotoxic lesions (NMDA) of the dorsal hippocampus (DH), the dorsal subiculum (DS), or both (DHDS), and controls were trained on a nonmatching-to-place task. Then, to identify the strategy used by each group, they were tested on the same task in the dark with the T-maze being rotated between the sample and the test runs. In the light, rats with combined lesions were impaired. In the dark, groups DH, DS, and controls performed near chance level except in trials without rotation, suggesting the use of a sense of direction. The same rats were trained on a radial-arm maze task. In the light, where proximal visual cues were accessible, combined lesions affected performance whereas in the dark, it was impaired by all lesions. This experiment demonstrated that the dorsal subiculum and the dorsal hippocampus play a crucial role in processing idiothetic information and/or in maintenance of this information in memory.     

Task-set reconfiguration suspends perceptual processing: evidence from semantic priming during the attentional blink

When two visual targets, Target 1 (T1) and Target 2 (T2), are presented among a rapid sequence of distractors, processing of T1 produces an attentional blink. Typically, processing of T2 is markedly impaired, except when T1 and T2 are adjacent (Lag 1 sparing). However, if a shift of task set--a change in task requirements from T1 to T2--occurs, this sparing is reduced substantially. With a semantic priming technique, in which T1 could be either related or unrelated to T2, the priming of T2 by T1 diminished markedly at Lag 1, when the transition between T1 and T2 involved a switch in either location (Experiments 1 and 2) or task (Experiment 3), but remained unaffected at other lags. These results suggest that perceptual processing of T2 cannot be carried out in parallel with task-set reconfiguration.     

Detecting group differences in sequential association using sampled permutations: Log odds,kappa, and phi compared

When determining whether a particular transition is more characteristic of one group than of another, two things are required: an index associated with the transition of interest and a statistical test that can determine whether group membership systematically affects values for that index. Here the familiar parametrict test is compared with a test based on sampled permutations. Indices considered are the odds and log odds ratio, Yule’sQ, Wampold’s (1989) transformed kappa, and phi. The odds and log odds ratio are monotonically increasing functions of Yule’sQ and so give similar results. Yule’sQ and phi are essentially rank order invariant and usually give similar results. Transformed kappa, however, rank orders subjects somewhat differently than the others; moreover, it appears somewhat biased. With respect to the tests, when subjects are 20 or more it does not matter much whether sampled permutation or parametrict tests are used; both yield essentially the same result. However, when subjects are fewer than 20, or whenever there is any other reason to think that parametric assumptions may not be met, permutation tests are recommended. A computer program that effects such tests is described.     

Spoken word recognition processes and the gating paradigm

Words varying in length (one, two, and three syllables) and in frequency (high and low) were presented to subjects in isolation, in a short context, and in a long context. Each word was presented repeatedly, and its presentation time (duration from the onset of the word) increased at each successive pass. After each pass, subjects were asked to write down the word being presented and to indicate how confident they were about each guess. In addition to replicating a frequency, a context, and a word-length effect, this “gating” paradigm allowed us to study more closely the narrowing-in process employed by listeners in the isolation and recognition of words: Some delay appears to exist between the moment a word is isolated from other word candidates and the moment it is recognized; word candidates differ in number and in type from one context to the other; and, like syntactic processing, word recognition is strewn with garden paths. The active direct access model proposed by Marslen-Wilson and Welsh is discussed in light of these findings.     

The perception of rate in spoken and sign languages

The methods of magnitude production and estimation were used to scale the perception of signing rate by signers and observers. As in the case of voice level and speech rate, the autophonic scale of signing rate has a slope greater than unity and is steeper than the corresponding extraphonic scale; the obtained exponents of the two power functions for signing are, respectively, 2.66 and 1.56. When English-speaking subjects estimated their own rate of reading of the translated version of the signed passage, they produced an autophonic reading scale quite similar to that for signing (exponent of 2.51), but when they made magnitude estimations of English rates covering the same range of rates as the signed passage, the exponent of the extraphonic reading scale was significantly larger (1.89). This was also the case when French subjects estimated French reading rates. The difference between extraphonic signing and reading scales was confirmed by subjects who knew no Sign Language or French; their results appear to indicate, in addition, that the processes involved in extraphonic perception of rate are purely acoustic (speech) or visual (sign) and do not require, as one could have thought, deeper linguistic operations.     

A study of timing in a manual and a spoken language: American sign language and English

A comparative analysis of the time variables in the production of speech and sign reveals that signers modify their global physical rate primarily by altering the time they spend articulating, whereas speakers do so by changing the time they spend pausing. When signers increase or decrease their pause time, however little they do so, they alter the number and the length of the pauses equally, whereas speakers primarily alter the number of pauses and leave their pause durations relatively constant. An analysis of the durations of signs reveals that signs are longer at the end of sentences than within sentences and that the first occurrence of a sign is longer than the second when syntactic location is controlled (both these findings have already been reported for spoken language). The inherent duration of a sign can be accounted for almost totally by the movement characteristic; handshape, location, and number of hands in a sign are of little importance. Finally, signers retain their regular quiet-breathing respiratory pattern across signing rates and inhale at locations independent of syntactic importance. In this they are quite unlike speakers, who breathe at syntactic breaks.This research was supported in part by Grant R03 MH 28133, Department of Health, Education, and Welfare.     

Regaining lost time: adult aging and the effect of time restoration on recall of time-compressed speech.

Two experiments in which time was restored to artificially accelerated (time-compressed) speech are reported. Experiment 1 showed that although both young and older adults' recall of the speech benefited from the restoration of time, time restoration failed to boost the older adults to their baseline levels for unaltered speech. In Experiment 2, either 100% or 125% of lost time was restored by inserting pauses, either at linguistic boundaries or at random points within the passages. Experiment 2 showed that the beneficial effects of time restoration depended on where processing time was inserted, as well as how much time was restored. Results are interpreted in terms of age-related slowing in speech processing moderated by preserved linguistic knowledge and short-term conceptual memory.     

Attention demands during reading and the occurrence of brief (express) fixations

Eye movements were recorded while subjects read passages of text repeatedly (Experiment 1) and while normal text and strings ofhomogeneous letters were fixated (Experiment 2). Text repetition decreased fixation durations and increased saccade size, presumably because it decreased attention demands. Irrespective ofrepetition, however, no distinct distribution of brief (express) fixations emerged. In Experiment 2, fixation durations were shorter and saccades were larger when strings of homogeneous letters were “read,” indicating that this condition decreased attention demands. Again, however, no distinct distribution of express fixations emerged. These findings pose problems for the view that attentional processes determine the occurrence of brief (express) fixation durations in reading. Supplementary analyses of Experiments 1 and 2 suggested that visuospatial processing affected fixation durations, irrespective of linguistic processing demands.