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T H Carr

Publications and source records attributed to T H Carr.

17 recordsLinked to original sources
PubMed1997

Expression of the Arabidopsis G-protein GP alpha1: purification and characterisation of the recombinant protein.

The Arabidopsis G alpha subunit, GP alpha1, was expressed within Escherichia coli by co-transformation with the expression vector and the dnaY gene which encodes tRNA(Arg)(AGA/AGG) Isolation of the recombinant GP alpha1 in a highly pure form could be achieved by a combination of anion exchange and dye affinity chromatography or by a single step affinity procedure via chromatography on 4-amino-anilido-GTP agarose. The recombinant protein yielded by both procedures was highly active and bound GTPgammaS with an apparent Kd in the nM range. GTPgammaS binding was stimulated two-fold in the presence of Zn2+ compared with that in the presence of Mg2+, Mn2+ or Ca2+.

Arabidopsis↗
PubMed1995

Automaticity and word perception: evidence from Stroop and Stroop dilution effects.

The Stroop effect is cut in half by adding a neutral word to the display. D. Kahneman and D. Chajczyk's (1983) "attention capture" account of "Stroop dilution" holds word recognition to be involuntary but strictly serial. The authors compared attention capture to 3 alternatives involving parallel rather than serial processing: In the lexicon, activation is divided among multiple words; postlexically, multiple words race for access to response processes; or prelexically, feature processing is degraded by multiple patterns whether or not they are words. Results support the latter. Multiple patterns are processed in parallel. If any are color words, Stroop effects occur but are reduced because any color word's input to lexical memory is lower in quality than if a single color word were the only pattern. Thus, lexical encoding is involuntary but can operate on several input representations in parallel, with effectiveness determined by input quality.

Adult↗
PubMed1992

Lexical access and the brain: anatomical constraints on cognitive models of word recognition.

Recent studies in the cognitive psychology of reading and many other skilled performances have been dominated by models inspired by neural connectivity (e.g., McClelland & Rumelhart, 1986). Such models have not yet begun to consider the accumulating evidence of considerable anatomical localization of component cognitive operations in the human brain (e.g., Posner, Petersen, Fox, & Raichle, 1988). In this article we apply anatomical findings to the job of building computational models of visual word recognition. Brain imaging studies already provide important constraints on how lexical access should be defined in terms of isolable encoding operations that compute the visual form, phonology, and semantics of words. Brain imaging studies also speak to issues of modularity versus interaction between these encoding operations, distribution versus localization of processing within the operations, and orchestration of operations to accomplish different word processing tasks. We conclude that a combined cognitive and anatomical analysis may be of considerable benefit in developing more adequate models of human information processing.

Brain↗
PubMed1992

Automaticity and cognitive anatomy: is word recognition "automatic"?

Recent progress in neural imaging technologies such as positron emission tomography and dense-array recording of event-related potentials has greatly increased the capacity for in vivo measurement of cognitively relevant processing activity within the human brain. Data from these neural imaging technologies can be combined with behavioral data from standard chronometric techniques to enhance computational modeling of human cognition. Applications of neural data to issues of attention and automaticity are illustrated in the domain of visual word recognition, addressing the question "Is word recognition automatic?"

Animals↗
PubMed1991

The level-of-focal-attention hypothesis in oral reading: influence of strategies on the context specificity of lexical repetition effects.

Two experiments examined the influence of level of focal attention--text or lexical--on benefits from lexical repetition in speeded oral reading of coherent texts and random word lists. Experiment 1 showed that with coherent targets, direction of attention to the text level resulted in benefit only from a previous reading of the same coherent paragraph. However, when attention was directed to the lexical level, equal benefit resulted from a previous reading of either the same coherent paragraph or a scrambled version of the paragraph. Experiment 2 showed that level of focal attention did not influence benefit with scrambled targets. Thus, the linguistic structure of the target is important to repetition benefits and their modulation by attentional strategies.

Analysis of Variance↗
PubMed1990

Adding new information to semantic memory: how much learning is enough to produce automatic priming?

A series of experiments investigated the integration of new vocabulary words into semantic memory and the creation of new associations between preexisting, but previously unrelated, words. The ability of the newly learned vocabulary words and associations to facilitate lexical decisions when serving as primes under conditions associated with automatic processing was used to index integration. The results indicate that very extensive study is necessary for such integration to occur and that it is easier to add a new word to semantic memory than to establish a link between two formerly unconnected words already in semantic memory. The implications of these results for models of semantic memory and the episodic/semantic distinction are considered.

Adult↗
PubMed1990

Semantic priming and repetition priming from masked words: evidence for a center-surround attentional mechanism in perceptual recognition.

Two lexical decision experiments compared semantic and repetition priming by masked words. Experiment 1 established prime-mask stimulus onset asynchronies (SOAs) with presence-absence detection judgments. Primes presented at detection-threshold SOAs produced equal facilitation for repeated and semantically related targets: 26 ms and 24 ms. Experiment 2 established SOAs with semantic judgments. Primes presented at 70% of the semantic-threshold SOA to mimic the exposure conditions of Experiment 1 produced slightly greater facilitation for repeated targets but a tendency toward inhibition for semantically related targets: 38 ms and -6 ms. These results confirm Dagenbach, Carr, and Wilhelmsen's (1989) report that strategies induced by threshold-setting tasks can influence masked priming. In addition, Experiment 2 suggests a mechanism for retrieving weakly activated semantic codes into consciousness that relies on the center-surround principle to enhance activation of sought-for codes and to inhibit related codes stored nearby in the semantic network.

Consciousness↗
PubMed1987

Strategic hand use preferences and hemispheric specialization in tactual reading: impact of the demands of perceptual encoding.

Four reading-related, information-processing tasks were administered to right-handed blind readers of braille who differed in level of reading skill and in preference for using the right hand or the left hand when required to read text with just one hand. The tasks were letter identification, same-different matching of letters that differed in tactual similarity, short-term memory for lists of words that varied in tactual and phonological similarity, and paragraph reading with and without a concurrent memory load of digits. The results showed interactions between hand preference and the hand that was actually used to read the stimulus materials, such that left preferrers were significantly faster and more accurate with their left hands than with their right hands whereas right preferrers were slightly but usually not significantly faster with their right hands than with their left hands. In all cases, the absolute magnitude of the left-hand advantage among left preferrers was substantially larger than the right-hand advantage among right preferrers. The results suggest that encoding strategies for dealing with braille are reflected in hand preference and that such strategies operate to modify an underlying but somewhat plastic superiority of the right hemisphere for dealing with the perceptual requirements of tactual reading. These requirements are not the same as those of visual reading, leading to some differences in patterns of hemispheric specialization between readers of braille and readers of print.

Adolescent↗
PubMed1982

Words, pictures, and priming: on semantic activation, conscious identification, and the automaticity of information processing.

We investigated the encoding mechanisms involved in the perceptual recognition of words and pictures. Latencies in naming word and picture targets were analyzed as a function of several characteristics of a preceding prime, including whether it was a word or a picture, its duration of exposure, the interval between the prime and target onset, and whether or not the prime was consciously identified and reported by the subject. Results indicated that a common semantic code is available that can represent the meaning of either a word or a picture. This semantic representation, however, appears to be more easily activated by picture primes than by word primes and seems to benefit the naming of picture targets more than the naming of word targets. Despite the advantage for pictures with respect to semantic activation, overall processing in the naming task was slower and more attention demanding for pictures than for words. Comparison of our data with data on classification, in which an opposite pattern occurs (overall processing appears to be slower and more attention demanding for words than for pictures), suggests that, on the average, pictures have faster and more automatic access to their meanings than to their names but that words have faster and more automatic access to their names than to their meanings. This conclusion concerning the relative ability of stimuli to activate different kinds of internal representations has implications for a theory of the basis and development of automaticity.

Discrimination Learning↗
PubMed1980

Early extraction of meaning from pictures and its relation to conscious identification.

Two experiments were conducted in which subjects labeled target pictures preceded by either semantically related or unrelated prime pictures. The exposure duration of each prime was varied around a threshold value, established separately for each subject, that represented the minimum viewing time necessary to identify the prime picture with 100% accuracy. The results of the first study indicated that semantic-priming effects can be obtained with pictures at prime exposure durations too brief for conscious identification of the prime to occur. Data from the second experiment provided an estimate of the minimum exposure time necessary for priming under these conditions. There was evidence from both experiments that attaching a name to a picture is an attended operation that can interfere with naming a subsequent picture, independent of any semantic priming that might occur. This indicates that extracting the meaning from a picture and consciously identifying it may be separate processes. The results are discussed in terms of current models of picture perception.

Adult↗
PubMed1979

Orthography and familiarity effects in word processing.

Both orthographic regularity and visual familiarity have been implicated as contributors to the efficiency of processing visually presented words. Our studies sought to determine which of the internal codes representing words in the nervous system are facilitated by these two variables. To do this, sets of letter strings in which orthography and familiarity were factorially combined were used as the basis for physical, phonetic, semantic, and lexical judgments. The data indicated consistent effects of orthography on the activation of all codes. These effects were seen in same-different matching and in judgments of stimulus orientation, which are based on visual codes; in judgments of pronounceability based on phonetic codes; in judgments of meaningfulness based on semantic codes; and in lexical decisions, which are based on phonetic and semantic codes together. Familiarity, on the other hand, had a clear influence on the activation of semantic codes and to a lesser extent affected phonetic codes. Despite previous positive results found in matching letter strings, however, no influence of familiarity occurred in judgments based on visual codes once evidence for criterion shifting was eliminated. Our negative results included direct tests of facilitation in matching acronyms (e.g., FBI) and in matching both regular and irregular strings familiarized by specific training. It now appears that earlier findings of visual familiarity effects may be attributed to response biases resulting from the activation of higher level codes sensitive to familiarity, and to the use of small sets of training stimuli that allowed subjects to induce orthographic-like rules. The results obtained so far with our methods seem to reconcile an inconsistent literature by showing that speeded decisions based on visual codes are most strongly influenced by rule-governed processing mechanisms sensitive to orthographic structure, whereas decisions based on phonetic and semantic codes are affected about equally by rule-governed mechanisms and by stimulus-specific mechanisms sensitive to familiarity. This conclusion may lead to changes in notions of how effective various kinds of visual training are likely to be at different stages in the acquisition of reading skill.

Discrimination Learning↗
PubMed1978

Perceptual flexibility in word recognition: strategies affect orthographic computation but not lexical access.

Four tachistoscopic forced-choice recognition experiments explored the flexibility of processes underlying word perception. Stimuli were words, orthographically regular but unfamiliar pseudowords, and orthographically irregular nonsense strings. In the first two experiments, subjects knew that several different kinds of stimuli would occur in each block of trials and that one kind would occur much more often than the others. No matter which stimulus subjects expected to see most often, accuracy on words and pseudowords differed little, and both were identified considerably better than nonsense. In the third and fourth experiments, subjects were led to believe that only on stimulus type would occur but were surreptitiously shown another type on a small number of trials. Words were again identified more accurately than nonsense, and the size of the effect was independent of expectations. However, when either words or nonsense strings were expected exclusively, pseudoword accuracy did not differ from nonsense accuracy. Only when subjects knew that pseudowords would occur did they identify pseudowords more accurately than nonsense. This dissociation between word and pseudoword identification indicates the operation of two independent encoding mechanisms during tachistoscopic recognition, a stimulus-specific or logogenlike system sensitive to particular familiar strings and an orthographic mechanism sensitive to generally applicable constraints on letter sequencing. The stimulus-specific mechanism appears to be utilized automatically, but use of the orthographic mechanism is under strategic control. As shown in the first two experiments, however, rather extraordinary measures were required to demonstrate the flexibility of the orthographic processes used in this task.

Cognition↗
PubMed1976

Perceptions of community life which distinguish between participants and nonparticipants in a neighborhood self-help organization.

Questionnaire, Edwards-Kirkpatrick scale, and semantic differential techniques were used to provide converging measures of psychosocial factors affecting participation in a community self-help organization. This group is attempting to maintain the racially mixed residential character of a neighborhood located in a zone of transition between large tracts of project housing and an area of stores, apartment buildings, and offices on the edge of a southern center city. Results indicate that a complexly integrated set of attitudes toward the area as a place to live, one's neighbors as active and potent yet stable people, and the future as a promising and secure time of life seems to determine attitudes toward and participation in the community organization.

Attitude↗