Biomedical subjects

A W Ellis

Publications and source records attributed to A W Ellis.

At least 37 records · Page 2Linked to original sources

PubMed1995

Individual mouse alpha-fetoprotein enhancer elements exhibit different patterns of tissue-specific and hepatic position-dependent activities.

Transcription of the mouse alpha-fetoprotein (AFP) gene, which is expressed at high levels in the visceral endoderm of the yolk sac and fetal liver and at low levels in the fetal gut, is regulated by three distinct upstream enhancer regions. To investigate the activities of these regions, each enhancer was individually linked to a heterologous human beta-globin promoter fused to the mouse class I H-2Dd structural gene. When tested in transgenic mice, the beta-globin promoter alone has minimal activity. We find that all three enhancers activate the beta-globin promoter in an AFP-like pattern; i.e., activity is detected in the yolk sac, fetal liver, and fetal gut. The enhancers remain active in the livers and guts of adult mice, consistent with previous studies showing that postnatal AFP repression is due not to the loss of enhancer activity but to a dominant repressor region. Enhancer III also functions in the brain. In addition, these studies reveal that the three enhancers exhibit different position-dependent activities in the adult liver. Enhancers I and II are most active in hepatocytes surrounding the central vein, with a gradual decrease in activity along the hepatic plates toward the portal triad. Enhancer III is active exclusively in hepatocytes surrounding the central vein. These data represent the first examples of individual control elements exhibiting positionally regulated activity in adult liver.

Animals↗

PubMed1994

Is "nonpropositional" speech preserved in aphasia?

Twenty-eight aphasic patients were tested on six tasks designed to assess "nonpropositional" speech and six matched tasks designed to assess propositional speech. The most reliable differentiation between nonpropositional and propositional speech type behaviors within a group of aphasics was found for the Numbers and Picture naming tasks. A smaller effect was observed on the Days of the week and Phrase repetition tasks. Only 6 of the 28 patients consistently showed a nonpropositional advantage across the range of task comparisons. However, a principal components analysis extracted two factors which differentiated propositional from nonpropositional tasks reasonably well. We conclude that nonpropositional speech, to the extent that it is measured by these tasks, is not preserved in aphasics as a group, though some patients may show a fairly consistent nonpropositional advantage. The distinction between propositional and nonpropositional speech does appear to have some application to aphasia, however. An error analysis supports the conjecture that propositional tasks involve semantic processing while nonpropositional tasks may place a greater load on phonological processing.

Aged↗

PubMed1994

The nature of semantic priming effects in the recognition of familiar people.

We report a series of experiments examining the nature of semantic priming effects in the recognition of familiar people. Experiment 1 showed that facilitation of the recognition of familiar target faces by related face primes occurs within the recognition system, since there is no equivalent priming when subjects are asked only to determine the sex of the target faces, rather than to recognize them as familiar. Experiments 2 and 3 examined the basis of the facilitatory effect of related primes, and showed that both for familiarity decision (Expt 2 and Expt 3) and face naming (Expt 3) tasks it is primarily based on close association of the prime and target people, rather than common membership of a semantic category. This associative component of semantic priming was further explored in Expt 4, which showed that cross-domain priming from face primes to target names was present for associated prime-target pairs, but was maximal when prime and target were the face (prime) and name (target) of the same person. The results of the experiments are consistent with the interactive activation simulation developed by Burton, Bruce & Johnston (1990), and set constraints which will have to be met by any other plausible account of semantic priming.

Face↗

PubMed1994

Effects of word frequency and age of acquisition on short-term memory span.

The experiments reported examine the effects of two highly related variables, word frequency and age of acquisition, on short-term memory span. Short-term memory span and speech rate were measured for sets of words which independently manipulated frequency and age of acquisition. It was found that frequency had a considerable effect on short-term memory span, which was not mediated by speech rate differences--although frequency did affect speech rate in one experiment. For age of acquisition, this situation was reversed; there was a small but significant effect of age of acquisition on speech rate, but no effect on memory span. This occurred despite results confirming that the stimuli used in the experiments produce an effect of age of acquisition on word naming. The results are discussed in terms of a two-component view of performance on short-term memory tasks.

Aging↗

PubMed1993

Impaired discrimination of familiar from unfamiliar faces.

We report investigations of the face processing abilities of J.T., a man who had suffered a right hemisphere stroke. J.T. showed a marked problem in discriminating between familiar and unfamiliar faces, with no corresponding problem in discriminating familiar from unfamiliar names. The problem with faces was still found 2 years after the stroke, but had resolved at long-term follow-up (9 years post stroke). When given unlimited time to respond, J.T. did not show any problem in recognising familiar faces, but tended to think that he recognised unfamiliar faces. When under time pressure, however, J.T. also failed to recognise a number of familiar faces which he could readily identify when the time pressure was removed. J.T.'s ability to remember a face and to think of other people who might be similar in appearance was affected by whether or not the face seemed familiar or unfamiliar to him. Hence, whatever underlay the spurious sense of familiarity was sufficient to produce real differences between the way in which genuinely unfamiliar and spuriously familiar faces were seen, leading us to suggest that his impaired discrimination of unfamiliar from familiar faces reflected a malfunction of face recognition units.

Aged↗

PubMed1993

Repetition priming and proper name processing. Do common names and proper names prime each other?

Three experiments are reported in which a repetition priming technique was used to investigate whether recognition of a person's surname which is also a known word (e.g. Baker) activates the lexical representation that mediates word recognition. Experiment 1 showed that a familiarity decision to familiar full names produced an effect of repetition priming on subsequent lexical decision to words that were presented in the initial task as surnames. Experiment 2 demonstrated that, conversely, a lexical decision primed subsequent familiarity decision to full names involving the same word. Experiment 3 showed that repeating the same decision during the initial and test phases did not produce a larger repetition priming effect than that obtained when the task at test differed from the prime task (name familiarity decision vs lexical decision or vice versa). The results are interpreted as support for the view that repetition priming is due to repeated activation of representations that are accessed by both common names and proper names.

Adult↗

PubMed1992

Cognitive mechanisms of face processing.

Evidence from natural and induced errors of face recognition, from the effects of different cues on resolving errors, and from the latencies to make different decisions about seen faces, all suggest that familiar face recognition involves a fixed, invariant sequence of stages. To recognize a familiar face, a perceptual description of a seen face must first activate a long-standing representation of the appearance of the face of the familiar person. 'Semantic' knowledge about such things as the person's occupation and personality are accessed next, followed, in the final stage, by the name. Certain factors affect the ease of familiar face recognition. Faces seen in the recent past are recognized more readily (repetition priming), as are distinctive faces, and faces preceded by those of related individuals (associative priming). Our knowledge of these phenomena is reviewed for the light it can shed upon the mechanisms of face recognition. Four aspects of face recognition--graded similarity effects and part-to-whole completion in repetition priming, prototype extraction with simultaneous retention of information about individual exemplars, and distinctiveness effects in classification and identification--are proposed as being compatible with distributed memory accounts of cognitive representations.

Association Learning↗

PubMed1992

Repetition priming follows spontaneous but not prompted recognition of familiar faces.

Reaction times to make a familiarity decision to the faces of famous people were measured after recognition of the faces in a pre-training phase had occurred spontaneously or following prompting with a name or other cue. At test, reaction times to familiar faces that had been recognized spontaneously in the pre-training phase were significantly facilitated relative to an unprimed comparison condition. Reaction times to familiar faces recognized only after prompting in the pre-training phase were not significantly facilitated. This was demonstrated both when a name prompt was used (Experiments 1 and 3) and when subjects were cued with brief semantic information (Experiment 2). Repetition priming was not found to depend on prior spontaneous recognition per se. In Experiment 3, spontaneously recognizing a familiar face did not prime subsequent familiarity judgements when the same face had only been identified following prompting on a prior encounter. In Experiment 4, recognition memory for faces recognized after cueing was found to be over 90% accurate. This indicates that prompted recognition does not yield repetition priming, even though subjects can remember the faces. A fusion of "face recognition unit" and "episodic record" accounts of the repetition priming effect may be more useful than either theory alone in explaining these results.

Cues↗

PubMed1992

Phonological priming of lexical retrieval in speech production.

We report a series of three experiments exploring phonological priming effects in speech production. In all cases, subjects repeated aloud auditorily presented primes and then named picture targets. Experiment 1 showed that targets were named faster when prime and target shared phonemes but only when these occupied the same word or syllabic positions. Experiment 2 showed that the degree of facilitation was unaffected by the lexicality of the prime or whether shared phonemes occurred early or late in the syllable. Experiment 3 examined the effect of the lexicality of the prime at different intervals between response and prime in an attempt to tease apart contributions to the effect from automatic and strategic processes. The results are considered in relation to current accounts of lexical retrieval.

Analysis of Variance↗

PubMed1992

Age of acquisition, not word frequency, affects object naming, not object recognition.

Word frequency is widely believed to affect object naming speed, despite several studies in which it has been reported that frequency effects may be redundant upon age of acquisition. We report, first, a reanalysis of data from the study by Oldfield and Wingfield (1965), which is standardly cited as evidence for a word frequency effect in object naming; then we report two new experiments. The reanalysis of Oldfield and Wingfield shows that age of acquisition is the major determinant of naming speed, and that frequency plays no independent role when its correlation with other variables is taken into account. In Experiment 1, age of acquisition and phoneme length proved to be the primary determinants of object naming speed. Frequency, prototypicality, and imageability had no independent effect. In Experiment 2, subjects classified objects into two semantic categories (natural or man-made). Prototypicality and semantic category were the only variables to have a significant effect on reaction time, with no effect of age of acquisition, frequency, imageability, or word length. We conclude that age of acquisition, not word frequency, affects the retrieval and/or execution of object names, not the process of object recognition. The locus of this effect is discussed, along with the possibility that words learned in early childhood may be more resistant to the effects of brain injury in at least some adult aphasics than words learned somewhat later.

Adult↗

PubMed1991

Understanding covert recognition.

An implementation of Bruce and Young's (1986) functional model of face recognition is used to examine patterns of covert face recognition previously reported in a prosopagnosic patient, PH. Although PH is unable to recognize overly the faces of people known to him, he shows normal patterns of face processing when tested indirectly. A simple manipulation of one set of connections in the implemented model induces behaviour consistent with patterns of results from PH obtained in semantic priming and interference tasks. We compare this account with previous explanations of covert recognition and demonstrate that the implemented model provides the most natural and parsimonious account available. Two further patients are discussed who show deficits in person perception. The first (MS) is prosopagnosic but shows no covert recognition. The second (ME) is not prosopagnosic, but cannot access semantic information relating to familiar people. The model provides an account of recognition impairments which is sufficiently general also to be useful in describing these patients.

Adult↗

PubMed1991

Analysis of the spontaneous writing errors of normal and aphasic writers.

Samples of spontaneous writing were collected from 150 normal subjects, 13 Broca's aphasics, 23 Wernicke's aphasics and 14 conduction aphasics. The errors obtained were classified using a system derived from investigations of slips of the pen in normal subjects. All three aphasic groups made a higher proportion of word-level errors than did the normal writers. Word-level errors tended to be selection errors (substitutions, blends, neologisms, and omissions) rather than movement errors (anticipations, perseverations and reversals). Conduction aphasics showed proportionately more letter movement and fewer letter selection errors than normal writers while Wernicke's and Broca's aphasics showed similar proportions. Graphic and phonetic similarity was no more important a determinant of letter errors in aphasics than in normals. The span of movement errors was particularly restricted in the Broca's and conduction aphasics. Asking patients to write connected text yields insight into the nature of the underlying disorder that could not be obtained from studying the writing of single words.

Agraphia↗

PubMed1991

Routes through the face recognition system.

Two experiments are reported which seek to examine the proposition first put forward by Hay and Young (1982), that recognition of a known person after seeing his or her face proceeds through a series of sequentially organized stages. In both experiments subjects were shown a selection of famous and unfamiliar faces and required to state whether each face was familiar. They were then asked to recall semantic information and the person's name. Of all the possible response types, only some are predicted by models derived from Hay and Young (1982), and only these responses were observed in Experiment 1. In order to give as complete an account as possible of the slips and errors made by subjects, they were interrogated some days after completing the testing phase in Experiment 2. As in the first experiment, the results supported the view that distinct but successive stages are involved in everyday face recognition. The method developed here provides an extension of the "dairy" type of study of everyday recognition errors into laboratory conditions, which confirms the findings of studies of everyday errors and provides strong support for sequential models.

Adult↗

PubMed1990

Repetition priming and face processing: priming occurs within the system that responds to the identity of a face.

A familiar stimulus that has recently been recognized will be recognized a second time more quickly and more accurately than if it had not been primed by the earlier encounter. This is the phenomenon of "repetition priming". Four experiments on repetition priming of face recognition suggest that repetition priming is a consequence of changes within the system that responds to the familiarity of a stimulus. In Experiment 1, classifying familiar faces by occupation facilitated subsequent responses to the same faces in a familiarity decision task (Is this face familiar or unfamiliar?) but not in an expression decision task (Is this face smiling or unsmiling?) or a sex decision task (Is this face male or female?). In Experiment 2, familiar faces showed repetition priming in a familiarity decision task, regardless of whether a familiarity judgment or an expression judgment had been required when the faces were first encountered. Expression decisions to familiar faces again failed to show repetition priming. In Experiment 3, familiar faces showed repetition priming in a familiarity decision task, regardless of whether a familiarity judgment or a sex judgment had been asked for when the faces were first encountered. Sex decisions to familiar faces again failed to show repetition priming. In Experiment 4, familiarity decisions continued to show repetition priming when a brief presentation time with encouragement to respond while the face was displayed reduced response latencies to speeds comparable to those for sex and expression judgments in Experiments 1 to 3. The results are problematic for theories that propose that repetition priming is mediated by episodic records of previous acts of stimulus encoding.

Adult↗

PubMed1990

Repetition priming from incomplete faces: evidence for part to whole completion.

Two experiments are reported in which subjects' reaction times to make familiarity decisions to the faces of famous people were compared for faces primed by previously seeing (1) the internal features of the same face, (2) the external features of the same face, or (3) a complete version of the same face. Reaction times to faces primed by the internal features, the external features or a complete face were significantly facilitated relative to an 'unprimed' comparison condition, and did not differ one from another. Viewing part of a familiar face on a previous occasion was therefore found to be as effective at priming recognition as seeing a whole face. This finding was demonstrated in Expt 1 for priming from the repetition of stimuli derived from an identical photograph of the same famous person, and in Expt 2 for priming from stimuli derived from a different photograph of the same familiar face. 'Distributed processing' accounts of repetition priming may be more useful than accounts based entirely on episodic records in explaining these results.

Adult↗

PubMed1989

Face processing and name retrieval in an anomic aphasic: names are stored separately from semantic information about familiar people.

Recent models of face recognition have proposed that the names of familiar people are accessed from a lexical memory store that is distinct from the semantic memory store that holds information about such things as a familiar person's occupation and personality. Names are nevertheless retrieved via the semantic system. If such models are correct, then it should be possible for a patient to have full access to semantic information about familiar people while being unable to name many of them. We report this pattern in an anomic aphasic patient, EST, whose inability to recall the names of familiar people occurred in the context of a general word-finding problem. EST showed a preserved ability to access semantic information from familiar faces, voices, and spoken and written names and to process facial expressions, but he was unable to name many familiar faces. These findings are compatible with current models of face processing and challenge models which propose that names are stored alongside semantic information in a general-purpose long-term memory store.

Anomia↗

PubMed1989

Loss of memory for people following temporal lobe damage.

A 40-yr-old woman, K.S., is reported, who shows a severe loss of memory for people following a history of epilepsy and right anterior temporal lobectomy. Despite this memory problem, K.S. is not clinically amnesic, has a Memory Quotient of 122 on the Wechsler Memory Scale in line with her IQ of 119, and performs well on conventional tests of recognition and recall. She does not have a generalized semantic memory deficit for living things, but her deficit extends beyond people to include famous animals, buildings and product names. Autobiographical memory is good, except where memory for people is concerned. The nature of the memory store that is impaired in K.S. is discussed, as are the implications of her case for theories of the organization of long-term memory.

Adult↗

PubMed1988

Modes of word recognition in the left and right cerebral hemispheres.

Four experiments are reported examining the effects of word length on recognition performance in the left and right visual hemifields (LVF, RVF). In Experiments 1 and 2 length affected lexical decision latencies to words presented in the LVF but not to words presented in the RVF. This result was found for both concrete and abstract nouns. Changing from a normal horizontal format to the use of unconventionally "stepped" words, however, produced length effects for words in both visual hemifields (Experiment 3). The Length x VHF interaction was found once again in Experiment 4 where subjects classified words as either concrete or abstract. A model proposing two modes of visual processing of letter strings is presented to account for these findings. Mode A operates independent of string length and is seen only in left hemisphere analysis of familiar words. Mode B is length dependent: it is the only mode possessed by the right hemisphere but is displayed by the left hemisphere to nonwords and to words in abnormal formats.

Cerebral Cortex↗