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At least 1,369 records · Page 76Linked to original sources
PubMed2001

Event-related functional magnetic resonance imaging study of the extrastriate cortex response to a categorically ambiguous stimulus primed by letters and familiar geometric figures.

Functional neuroimaging studies have suggested a specific role of the extrastriate cortex in letter string and visual word form processing. However, this region has been shown to be involved in object recognition and its specificity for the processing of linguistic stimuli may be questioned. The authors used an event-related functional magnetic resonance imaging design with category priming to record the response elicited by the passive viewing of single letters, geometric figures, and of the categorically ambiguous stimulus "O" that pertains to both sets of familiar symbols. Bilateral activations in the extrastriate cortex were found, with a left predominance particularly pronounced for the ambiguous stimulus. Individual analysis of spatial extent and signal intensity showed a priming x stimulus x hemisphere interaction. When primed by the congruous categoric set, a bilateral decrease in activation was observed for letters and geometric figures. The ambiguous stimulus behaved as a letter for the left hemisphere, with decreased activation when primed by letters, whereas in the right hemisphere, an adaptation effect occurred when primed by geometric figures. These priming effects suggest that, for the ambiguous stimulus, letter processing was systematically involved in the left extrastriate cortex. The current results support the existence of a neural substrate for the abstract category of letters.

Adult↗
PubMed1989

Anthropometric dimensions and overuse injury among Australian keyboard operators.

This study was instigated to examine the relationship between overuse injury and anthropometric dimensions of Australian keyboard operators to investigate the possibility that a poor anthropometric fit of the workstation may result in greater incidence of such disorders. There were no differences between the anthropometric dimensions of sufferers and nonsufferers of overuse injury among the male keyboard operators. Among men in this study, stature and several other anthropometric dimensions as a proportion of stature were similar to those of North American and European populations for which equipment used in Australia is designed. In contrast, among women, significant differences were evident between sufferers and nonsufferers. The sufferers had greater hip widths and seat breadths, and a greater proportion were overweight (body mass greater than 26). There was also a tendency for shorter limb segment lengths among the sufferers. The women as a group, and the sufferers in particular, had several anthropometric dimensions that, as a proportion of stature, were outside the range of reference populations for design of Australian office workstations. The subject numbers in the present study are relatively small; however, they suggest that a proportion of the female population may not be accommodated by equipment currently in use. The increased proportion of sufferers who are overweight may suggest a relationship between overuse injury and lack of exercise, since the latter is well known to cause increased weight. A longitudinal study is needed to confirm this observation.

Adult↗
PubMed2003

Modeling open-set spoken word recognition in postlingually deafened adults after cochlear implantation: some preliminary results with the neighborhood activation model.

HYPOTHESES: Do cochlear implants provide enough information to allow adult cochlear implant users to understand words in ways that are similar to listeners with acoustic hearing? Can we use a computational model to gain insight into the underlying mechanisms used by cochlear implant users to recognize spoken words? BACKGROUND: The Neighborhood Activation Model has been shown to be a reasonable model of word recognition for listeners with normal hearing. The Neighborhood Activation Model assumes that words are recognized in relation to other similar-sounding words in a listener's lexicon. The probability of correctly identifying a word is based on the phoneme perception probabilities from a listener's closed-set consonant and vowel confusion matrices modified by the relative frequency of occurrence of the target word compared with similar-sounding words (neighbors). Common words with few similar-sounding neighbors are more likely to be selected as responses than less common words with many similar-sounding neighbors. Recent studies have shown that several of the assumptions of the Neighborhood Activation Model also hold true for cochlear implant users. METHODS: Closed-set consonant and vowel confusion matrices were obtained from 26 postlingually deafened adults who use cochlear implants. Confusion matrices were used to represent input errors to the Neighborhood Activation Model. Responses to the different stimuli were then generated by the Neighborhood Activation Model after incorporating the frequency of occurrence counts of the stimuli and their neighbors. Model outputs were compared with obtained performance measures on the Consonant-Vowel Nucleus-Consonant word test. Information transmission analysis was used to assess whether the Neighborhood Activation Model was able to successfully generate and predict word and individual phoneme recognition by cochlear implant users. RESULTS: The Neighborhood Activation Model predicted Consonant-Vowel Nucleus-Consonant test words at levels similar to those correctly identified by the cochlear implant users. The Neighborhood Activation Model also predicted phoneme feature information well. CONCLUSION: The results obtained suggest that the Neighborhood Activation Model provides a reasonable explanation of word recognition by postlingually deafened adults after cochlear implantation. It appears that multichannel cochlear implants give cochlear implant users access to their mental lexicons in a manner that is similar to listeners with acoustic hearing. The lexical properties of the test stimuli used to assess performance are important to spoken-word recognition and should be included in further models of the word recognition process.

Adult↗
PubMedDate not supplied

Learning directions of objects specified by vision, spatial audition, or auditory spatial language.

The modality by which object azimuths (directions) are presented affects learning of multiple locations. In Experiment 1, participants learned sets of three and five object azimuths specified by a visual virtual environment, spatial audition (3D sound), or auditory spatial language. Five azimuths were learned faster when specified by spatial modalities (vision, audition) than by language. Experiment 2 equated the modalities for proprioceptive cues and eliminated spatial cues unique to vision (optic flow) and audition (differential binaural signals). There remained a learning disadvantage for spatial language. We attribute this result to the cost of indirect processing from words to spatial representations.

Adult↗
PubMed2004

An asynchronously controlled EEG-based virtual keyboard: improvement of the spelling rate.

An improvement of the information transfer rate of brain-computer communication is necessary for the creation of more powerful and convenient applications. This paper presents an asynchronously controlled three-class brain-computer interface-based spelling device [virtual keyboard (VK)], operated by spontaneous electroencephalogram and modulated by motor imagery. Of the first results of three able-bodied subjects operating the VK, two were successful, showing an improvement of the spelling rate sigma, the number of correctly spelled letters/min, up to sigma = 3.38 (average sigma = 1.99).

Algorithms↗
PubMed2002

A modified Perkins Brailler for text entry into windows applications.

In this paper, we describe how a Perkins Brailler can be adapted so that it can function as a keyboard to a personal computer. The paper describes the earlier work of others and the hardware and software of our system and concludes with indications of how the system may be improved.

Blindness↗
PubMed2003

"Virtual keyboard" controlled by spontaneous EEG activity.

A "virtual keyboard" (VK) is a letter spelling device operated for example by spontaneous electroencephalogram (EEG), whereby the EEG is modulated by mental hand and leg motor imagery. We report on three able-bodied subjects, operating the VK. The ability in the use of the VK varies between 0.85 and 0.5 letters/min in error-free writing.

Algorithms↗
PubMed2004

Producing preferred format material from Microsoft Word.

This paper presents a set of tools that are integrated with a word processor to produce documents in a visually impaired person's "preferred format." The paper considers the motivation for producing such tools and describes tools to perform spoken transcription (to cassette tape) and intelligent large print production.

Communication Devices for People with Disabilities↗
PubMed2004

Conversion of EEG activity into cursor movement by a brain-computer interface (BCI).

The Wadsworth electroencephalogram (EEG)-based brain-computer interface (BCI) uses amplitude in mu or beta frequency bands over sensorimotor cortex to control cursor movement. Trained users can move the cursor in one or two dimensions. The primary goal of this research is to provide a new communication and control option for people with severe motor disabilities. Currently, cursor movements in each dimension are determined 10 times/s by an empirically derived linear function of one or two EEG features (i.e., spectral bands from different electrode locations). This study used offline analysis of data collected during system operation to explore methods for improving the accuracy of cursor movement. The data were gathered while users selected among three possible targets by controlling vertical [i.e., one-dimensional (1-D)] cursor movement. The three methods analyzed differ in the dimensionality of the cursor movement [1-D versus two-dimensional (2-D)] and in the type of the underlying function (linear versus nonlinear). We addressed two questions: Which method is best for classification (i.e., to determine from the EEG which target the user wants to hit)? How does the number of EEG features affect the performance of each method? All methods reached their optimal performance with 10-20 features. In offline simulation, the 2-D linear method and the 1-D nonlinear method improved performance significantly over the 1-D linear method. The 1-D linear method did not do so. These offline results suggest that the 1-D nonlinear or the 2-D linear cursor function will improve online operation of the BCI system.

Adult↗
PubMedDate not supplied

The development of word retrieval abilities in the second year and its relation to early vocabulary growth.

The present research investigated the development of word retrieval abilities late in the second year when most children display a marked increase in word production. When asked what was hidden in a given box, children with still quite limited productive vocabularies were reliably less likely to produce the labels of the hidden objects than were children with larger productive vocabularies even though (1) all children could name those objects and (2) all children did well when asked to find those same hidden objects. Additionally, the provision of pictorial cues facilitated word retrieval, especially in the early stage of lexical development. Naming errors during a naturalistic book-reading session peaked in children whose productive vocabularies had recently begun to expand, further suggesting that word retrieval processes undergo significant changes at this time.

Child Language↗
PubMed1995

Auditory and visual semantic priming using different stimulus onset asynchronies: an event-related brain potential study.

Semantic priming effects (behavioral and electrophysiological) were compared in the visual and auditory modalities across three stimulus onset asynchronies (SOAs; 0, 200, and 800 ms). When both prime and target were presented in the visual modality (the prime just to the left of a fixation point and the target to the right), there were N400 priming effects present across the three SOAs. However, the N400 in the 0-ms SOA condition extended longer in time (800 vs. 500 ms) than in the other SOAs. When both the prime and target were presented in the auditory modality (the prime to the right ear and the target to the left), the largest priming effects were found for the 800-ms SOA. Moreover, there was a relatively early priming effect present in the 0- and 800-ms SOA conditions but not in the 200-ms condition. The results are discussed in terms of modality differences in the time course of word comprehension processes.

Adolescent↗
PubMed2006

Geriatrics.

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Geriatrics↗