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.

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.

Cross-modal priming evidence for phonology-to-orthography activation in visual word recognition.

Subjects were asked to indicate which item of a word/nonword pair was a word. On critical trials the nonword was a pseudohomophone of the word. RTs of dyslexics were shorter in blocks of trials in which a congruent auditory prime was simultaneously presented with the visual stimuli. RTs of normal readers were longer for high frequency words when there was auditory priming. This provides evidence that phonology can activate orthographic representations; the size and direction of the effect of auditory priming on visual lexical decision appear to be a function of the relative speeds with which sight and hearing activate orthography.

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.

Aphasia diagrams: a new notational scheme for representing neurolinguistic deficits.

Models of language processing are becoming extremely complex. As a result, it has become very difficult to develop a thorough understanding of even a single patient's deficits, let alone to represent those deficits in a way which renders their significance apparent to others. In this paper, we describe and demonstrate the use of a notational system which has been developed specifically for representing the complexities of neurolinguistic deficits. The notational system is simple to learn and to use and may easily be extended and adapted to different models of language processing. It may also be used to represent the results from other nonlinguistic neuropsychological batteries which are composed of tightly interdependent subtests with many related factors included in each subtest. Despite its simplicity, the notational system has proven itself in the field as a useful tool for rendering complex deficits more easily interpretable.

Primary progressive aphasia: a review of 112 cases.

Primary progressive aphasia (PPA) was first recognized by Mesulam in 1982. Although dozens of cases have since been described, it has been difficult to place these cases into a coherent framework due to the wide variation in measures which have been reported. We review 170 contacts with 112 patients to provide a clinical, neuroanatomical, and neuropsychological profile of patients with the disorder. The progression of the disease is analyzed over a 10-year reporting period starting from symptom onset to show how progression affects five general linguistic skills: oral and written naming, reading, repetition, and general comprehension. The pattern of functional and neurological deficits in PPA is heterogeneous. Differences in the distribution of neurological anomalies between patients with bilateral and unilateral changes suggest that there may be two separate disease processes involved.

On the status of object concepts in aphasia.

While verbal comprehension is often impaired in aphasia due to left hemispheric damage, the status of nonverbal conceptual knowledge of objects remains controversial. We tested 16 aphasic subjects for their comprehension of concrete single words. Eight showed significant impairment on word-to-picture matching, when distractors were semantically and not just perceptually confusable. These 8 also made errors in answering verbal probe questions concerning the same items. When tested on a nonverbal pictorial version of the same probe questions, however, 3 of these 8 improved their performance to the level of normal controls. The other 5 showed continuing impairment in indicating responses to pictorial probes. These 5 showed no evidence of generalized intellectual impairment, and it is concluded that they demonstrated a comprehension deficit not limited to the verbal domain. Unlike the other aphasic patients, these latter 5 also had CT scan lesions extending into the posterior left temporal lobe (involving Brodmann's areas 22, 21, and 37). They were also more impaired in terms of general aphasia severity. It is suggested that a nonverbal (as well as verbal) semantic memory deficit occurs in a subgroup of patients with single word comprehension disturbance due to aphasia, and this may reflect general severity of language impairment as well as damage to certain localized brain regions.

The neural substrate for concrete, abstract, and emotional word lexica a positron emission tomography study.

Viewing of single words produces a cognitively complex mental state in which anticipation, emotional responses, visual perceptual analysis, and activation of orthographic representations are all occurring. Previous PET studies have produced conflicting results, perhaps due to the conflation of these separate processes or the presence of subtle differences in stimulus material and methodology. A PET study of 10 normal individuals was carried out using the bolus H2(15)O intravenous injection technique to examine components of processing of passively viewed words. Subjects viewed blocks of random-letter strings or abstract, concrete, or emotional words (words with positive or negative emotional salience). Baseline conditions were either passive viewing of plus signs or an anticipatory state (viewing plus signs after being warned to expect words or random letters to appear imminently). All words (and to a lesser extent the random letters) produced robust activation of cerebral blood flow in the left posterior temporal lobe, in addition to bilateral occipital activation. Furthermore, emotional words produced activation in orbital and midline frontal structures. Further activation in the left orbital frontal gyrus, the left inferior temporal gyrus, the left caudate nucleus, the anterior cingulate, and the cerebellum could be ascribed to the anticipatory state. This pattern of activity suggests that the occipital regions are recruited for visual-perceptual analysis of words, and the left temporal lobe represents the neural substrate for the orthographic lexicon. In addition, emotionally relevant material produces further processing in limbic brain structures of the frontal lobes. Detailed analysis of the task therefore substantially clarifies the neuroanatomic basis of single-word processing.

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.

Increased semantic priming in patients with dementia of the Alzheimer's type.

Semantic priming on a lexical decision task(LDT) was examined in 50 patients with mild to moderate dementia of the Alzheimer's Type(DAT), and 25 normal age-matched controls. DAT patients were slower in their responses, and showed significantly greater priming effects (mean 54 ms vs. 27 ms in controls). The size of the priming effect correlated with the speed of response on the LDT task for the individual DAT patients but not for controls. Twenty of the DAT patients (vs. one control) showed priming greater than 60 ms. This subgroup of DAT patients with "hyperpriming" was slower than the nonhyperpriming group on "yes" responses to targets preceded by unassociated prime words and more impaired on tests of clock drawing and verbal fluency. Slowing of responses alone, however, seems unable to account for the presence of increased priming in DAT patients. Its presence may reflect semantic memory deficits, as well as impaired attentional processing and supervisory control systems. The exact mechanism of this increased priming remains to be established.

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.

Hemorrhage following colonoscopic polypectomy.

Clinically significant hemorrhage following colonoscopic polypectomy may occur primarily as the polyp is removed or manifest itself days to weeks later secondary to clot dissolution. The rate of hemorrhage following colonoscopic polypectomy ranges widely from 0.3 to 6.1 percent, depending on whether the data are derived from studies using the number of patients or number of polypectomies. A retrospective study was performed in our institution to study 4,721 patients who underwent polypectomy between January 1987 and December 1991. Twenty (0.4 percent) of these patients required hospital admission because of 9 primary and 11 delayed hemorrhages. Fifty-four polyps were removed from these patients: 11 in the right colon, 7 in the transverse colon, 17 in the descending colon, and 19 in the sigmoid colon. Eight polyps were 2 cm or larger, 10 were pedunculated, and 44 were sessile. Six patients underwent cauterization or resnaring of the bleeding polyp site, one patient underwent subtotal colectomy, and the remainder of the patients stopped bleeding spontaneously. Factors that could be associated with the outcome of hemorrhage include patient age, size, location, number and morphology of polyps (i.e., sessile or thick stalk), and use of anticoagulants. An experienced endoscopist with knowledge of electrosurgical and technical principles may be the most important factor for prevention of postpolypectomy bleeding.

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.

Modulation of the directional attention deficit in visual neglect by hemispatial factors.

Using a visuo-spatial cuing paradigm, Posner and collaborators (Posner, Cohen, & Rafal, 1982; Posner, Walker, Friedrich, & Rafal, 1984) reported that subjects with a parietal lobe lesion have difficulty in disengaging their visual attention from an invalidly precued location in the ipsilesional hemifield when the target they have to respond to is presented in the contralesional field. Later, these authors (Posner, Walker, Friedrich, & Rafal, 1987) proposed that this disengagement deficit is one involving spatial shifts of attention in a contralesional direction, irrespective of the visual hemifield in which the target is presented. This proposal of a directional disengagement deficit along the horizontal axis, present in either hemifield, contrasts with a report by Baynes, Holtzman, & Volpe (1986) showing, in right parietal subjects, a disengagement deficit for shifts of attention along the vertical axis that is only manifest in the contralesional hemifield. In the present report, we assessed the disengagement deficit of a neglect subject along the horizontal and vertical axes. Results show a disengagement deficit restricted to shifts of attention in the contralesional direction (horizontal axis), which is significant only in the contralesional visual hemifield. However, there is a clear trend for a directional disengagement deficit in the ipsilateral field. These observations indicate that the attention deficit present in neglect is directional and is modulated either by hemispatial factors or by the lateral target location in the visual field. On the basis of the present results, it is proposed that the deficit of parietal subjects may best be conceptualized as one of attentional capture for stimuli located on the contralesional side of the current focus of attention rather than one of disengagement.

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.

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.

Language localization with activation positron emission tomography scanning.

We report the first instance of the use of 3-dimensional magnetic resonance imaging anatomically correlated to positron emission tomography (PET) scanning to identify language areas in a patient with an arteriovenous malformation (AVM) in the posterior speech region. The patient was a 24-year-old right-handed woman with an angiographically proven AVM (3-4 cm) in the left mid-posterior second temporal convolution in whom a left intracarotid injection of sodium Amytal produced significant language disruption. A baseline PET cerebral blood flow study identified the AVM, and an activation PET scan performed during the reading and speaking of simple words showed increased activity in the left parastriate cortex (the second visual area), in the left posterior third frontal convolution (Broca's area), and in the left inferior and midtemporal gyri (Wernicke's area). Increased activity was also noted in the right and left transverse temporal (Heschl's) gyri, in the left precentral gyrus, in the left medial superior frontal gyrus (the supplementary motor area), and in the right cerebellum. We conclude that activation PET scanning is useful in the preoperative assessment of patients who harbor cerebral AVMs in classically described speech regions.

Anatomical mapping of functional activation in stereotactic coordinate space.

Numerous applications have been reported for the stereotactic mapping of focal changes in cerebral blood flow during sensory and cognitive activation as measured with positron emission tomography (PET) subtraction images. Since these images lack significant anatomical information, analysis of these kinds of data has been restricted to an automated search for peaks in the PET subtraction dataset and localization of the peak coordinates within a standardized stereotactic atlas. This method is designed to identify isolated foci with dimensions smaller than the image resolution. Details of activation patterns that may extend over finite distances, following the underlying anatomical structures, will not be apparent. We describe the combined mapping into stereotactic coordinate space of magnetic resonance imaging (MRI) and PET information from each of a set of subjects such that the major features of the activation pattern, particularly extended tracts of increased blood flow, can be immediately assessed within their true anatomical context as opposed to that presumed using a standard atlas alone. Near areas of high anatomical variability, e.g., central sulcus, or of sharp curvature, e.g., frontal and temporal poles, this information can be essential to the localization of a focus to the correct gyrus or for the rejection of extracerebral peaks. It also allows for the removal from further analysis of data from cognitively-normal subjects with abnormal anatomy such as enlarged ventricles. In patients with neuropathology, e.g., Alzheimer's disease, arteriovenous malformation, stroke, or neoplasm, the use of correlated MRI is mandatory for correct localization of functional activation.