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Biomedical subjects

D N Bub

Publications and source records attributed to D N Bub.

11 recordsLinked to original sources
PubMed2001

Interference from related items in object identification.

Interference between related items in the identification of objects was examined using a postcue procedure. Pairs of objects were presented as differently colored line drawings followed by a color cue to indicate which object to name. Naming latencies were longer when both objects were from the same superordinate category than when they were unrelated. This interference effect was replicated when subjects were cued to report the color of a drawing rather than its name. Interference was greatly reduced when more distinctive attributes were used to distinguish members of a pair, both when the task required naming an object and when it required report of an object's attribute. These results challenge accounts of interference in the postcue paradigm that are based on competitive interactions in the activation of phonological representations by semantics and instead implicate object-attribute integration in memory as the source of interference.

Adult↗
PubMed1999

Object identification deficits in dementia of the Alzheimer type: combined effects of semantic and visual proximity.

Identification deficits in dementia of the Alzheimer Type (DAT) often target specific classes of objects, sparing others. Using line drawings to uncover the etiology of such category-specific deficits may be untenable because the underlying shape primitives used to differentiate one line drawing from another are unspecified, and object form is yoked to object meaning. We used computer generated stimuli with empirically specifiable properties in a paradigm that decoupled form and meaning. In Experiment 1 visually similar or distinct blobs were paired with semantically close or disparate labels, and participants attempted to learn these pairings. By having the same blobs stand for semantically close and disparate objects and looking at shape-label confusion rates for each type of set, form and meaning were independently assessed. Overall, visual similarity of shapes and semantic similarity of labels each exacerbated object confusions. For controls, the effects were small but significant. For DAT patients more substantial visual and semantic proximity effects were obtained. Experiment 2 demonstrated that even small changes in semantic proximity could effect significant changes in DAT task performance. Labeling 3 blobs with "lion," "tiger," and "leopard" significantly elevated DAT confusion rates compared to exactly the same blobs labeled with "lion," "tiger," and "zebra." In conclusion both visual similarity and semantic proximity contributed to the identification errors of DAT patients.

Aged↗
PubMed1998

Semantic and visual determinants of face recognition in a prosopagnosic patient.

Prosopagnosia is the neuropathological inability to recognize familiar people by their faces. It can occur in isolation or can coincide with recognition deficits for other nonface objects. Often, patients whose prosopagnosia is accompanied by object recognition difficulties have more trouble identifying certain categories of objects relative to others. In previous research, we demonstrated that objects that shared multiple visual features and were semantically close posed severe recognition difficulties for a patient with temporal lobe damage. We now demonstrate that this patient's face recognition is constrained by these same parameters. The prosopagnosic patient ELM had difficulties pairing faces to names when the faces shared visual features and the names were semantically related (e.g., Tonya Harding, Nancy Kerrigan, and Josee Chouinard -three ice skaters). He made tenfold fewer errors when the exact same faces were associated with semantically unrelated people (e.g., singer Celine Dion, actress Betty Grable, and First Lady Hillary Clinton). We conclude that prosopagnosia and co-occurring category-specific recognition problems both stem from difficulties disambiguating the stored representations of objects that share multiple visual features and refer to semantically close identities or concepts.

Aged↗
PubMed1995

Visual word activation in pure alexia.

A patient with pure alexia (DM) is shown to perform rapid and accurate lexical decisions for common words without the ability to recover their complete identity. We provide evidence using a speeded decision task that DM is not forced to rely on a laborious analysis of individual letter forms when judging the lexical status of orthographic patterns varying in length, though he clearly must use this approach to fully identify a word for explicit report. By contrast, the ability to rapidly classify a word apparently does not extend to judgements of its superordinate category. DM makes semantic decisions for visual words by adopting the same inefficient procedure he uses for verbal report of their identity. The results provide further constraints on the functional deficit responsible for pure alexia. We argue that DM is able to monitor the overall activation of word units without achieving full identification and that such a process may be a characteristic of the normal reading mechanism.

Adult↗
PubMed1994

Pure alexia: attempted rehabilitation and its implications for interpretation of the deficit.

On the basis of data indicating the failure to encode letters as abstract orthographic identities in a pure alexic patient (D.M.) coupled with hypotheses about the effect of such a failure on word reading, an attempt at changing the nature of letter processing in D.M. was conducted. The training procedures failed to produce any fundamental change in the operations used by D.M. to encode isolated letters or words. However, rapid and massive benefits occurred in the overall speed of reading as a result of the training program. These appear to result from an increased rate of letter identification and the faster integration of individual letters into letter combinations. The observations gathered throughout this rehabilitation attempt provided evidence which constrains the range of possible explanations for the characteristic features of pure alexia. It is proposed that the letter-by-letter reading procedure which is the hallmark of the disorder may follow from an incapacity to directly encode visual letters as abstract orthographic types.

Adult↗
PubMed1993

Jules Dejerine and his interpretation of pure alexia.

Dejerine's interpretation of pure alexia is routinely mentioned in all neuropsychological textbooks, yet the details of his account and the evidence on which it is based have never been subjected to a critical analysis. We provide such an evaluation in this paper, summarizing the behavioral data that Dejerine presented in his now famous case report and the theoretical framework he adopted to explain the phenomenon of alexia without agraphia. We also provide a link between Dejerine's work and current hypotheses on the nature of the syndrome.

Brain↗
PubMed1993

Single-character processing in a case of pure alexia.

The processing of single characters in a pure alexic patient was studied in an attempt to identify the impairment responsible for his reading disorder. Observations from Experiments 1 to 4 suggested a deficit of identification of alphanumeric stimuli without any impairment affecting the elaboration of a structural description of visual stimulation. Experiment 5 indicated that the identification disorder results from a defect in the selective processes--activation and/or inhibition--that must come into play for achieving an appropriate match between a structural description of the stimulation and representations of the identities of known stimuli. The possible implications of this deficit in single-character identification for word reading are discussed.

Adult↗
PubMed1993

Evidence for an independent stimulus-centered spatial reference frame from a case of visual hemineglect.

Previous experiments with patients suffering from visual hemineglect have provided evidence relevant to the organization of the human spatial representation system. We examined the hypothesis that one reference frame used to represent the location of objects in the environment is based on the spatial extent of the stimulation that needs to be processed at a specific point in time; in current terminology, a stimulus-centered reference frame. The paradigm used was one of filtering, and variation of the location of the target within a horizontal array of items (stimulus-relative location) was independent of the target location relative to the subject and to stable reference points in the environment. Results showed that stimulus-relative target location provided an independent contribution to the magnitude of the neglect symptoms. This is taken as an indication that a stimulus-centered spatial reference frame contributes to the representation of the location of visual objects in human vision and that this representation may serve to direct visual attention.

Aged↗
PubMed1989

Word recognition and orthographic context effects in a letter-by-letter reader.

The performance of letter-by-letter readers when attempting to decipher written material gives the impression that words fail to directly evoke any higher-level representation. As a consequence, spelling patterns appear to be treated perceptually as if they were a collection of random letters. We tested the hypothesis that words are no longer mapped onto orthographic descriptions by examining the ability of a letter-by-letter reader to identify letters in familiar words, pseudowords, and random strings. A clear effect of orthographic context was obtained on the accuracy of letter recognition, indicating that spelling patterns do gain access to more central components of the reading mechanism. The implications of this result for our understanding of the syndrome are discussed.

Attention↗
PubMed1988

Different modes of word recognition in the left and right visual fields.

We confirm previous evidence indicating that word length has a substantial effect on word recognition in the LVF but a much weaker effect in both the RVF and fovea. The nature of encoding in the LVF is not altered when the words are vertically displayed (Experiment 2), and the effect cannot therefore be entirely due to scanning artefact or acuity gradients in peripheral vision. We provide evidence that links the asymmetrical influence of word length directly to hemispheric specialization: left-handers, who as a group are much less consistently lateralized than right-handers are also less affected by word length in the LVF on the average (Experiment 3). This occurs because the asymmetry for certain left-handers is either very weak or, in some cases, is the complete reverse of the asymmetry observed in right-handers. Finally, we demonstrate that the length x field interaction is observed in lexical decisions (Experiment 4) which do not entail pronunciation of written words. There is some indication that concrete, high-imageable words produce a smaller effect of length in the LVF than abstract, low-imageable words, and we discuss this outcome in relation to the proposal that the right hemisphere can sometimes extract a lexical code from letter information. The concept of distinct modes of word recognition in the LVF and RVF clarifies a number of issues in laterality research, and suggests a new approach to evaluating group differences in half-field performance.

Adult↗