Biomedical subjects

G C Baylis

Publications and source records attributed to G C Baylis.

36 records · Page 2Linked to original sources

PubMed1992

Preserved figure-ground segregation and symmetry perception in visual neglect.

A central controversy in current research on visual attention is whether figures are segregated from their background preattentively, or whether attention is first directed to unstructured regions of the image. Here we present neurological evidence for the former view from studies of a brain-injured patient with visual neglect. His attentional impairment arises after normal segmentation of the image into figures and background has taken place. Our results indicate that information which is neglected and unavailable to higher levels of visual processing can nevertheless be processed by earlier stages in the visual system concerned with segmentation.

Aged↗

PubMed1992

Selective reaching: evidence for action-centered attention.

Most studies of selective attention briefly present static 2-dimensional stimuli and require arbitrary responses such as verbal naming or a keypress. Many of our perceptual-motor interactions with the environment, however, require reaching directly toward an object while ignoring other objects in the scene. A series of experiments examines selective attention in the latter reaching situation. Effects previously observed in the traditional experimental procedures were obtained, suggesting that the models developed (which propose inhibitory mechanisms, e.g.) apply to ecologically valid situations. Attention accesses action-centered internal representations during such tasks.

Adult↗

PubMed1992

Movement and proximity constrain miscombinations of colour and form.

A relatively frequent error when reporting brief visual displays is to combine presented features incorrectly. It has been proposed that Gestalt grouping constrains such errors so that miscombined features tend to come from the same perceptual group. In three experiments it was examined whether this principle applies to grouping by motion, and to grouping by proximity. Miscombinations of colour and form were more likely to consist of a colour and form that had moved in the same direction than features which had moved in opposite directions. Miscombinations were also more likely for adjacent items. The implications of these results for the mechanisms of feature integration are discussed.

Adult↗

PubMed1992

Visual parsing and response competition: the effect of grouping factors.

When the task is to categorize a target letter at a known location, subjects show more interference from incongruent distractors that are relatively close (B. A. Eriksen & C. W. Eriksen, 1974) or that share common motion with the target (Driver & Baylis, 1989). In eight experiments, we examined whether static factors other than proximity can affect the amount of interference. When distractors and the target letter were in the same color, the distractors interfered more than they did when they were in a different color, even when the latter were closer to the target. Good continuation between the target and distractors also led to more interference. These results suggest that the efficiency of selection is determined by several aspects of the relation between targets and distractors in addition to their proximity, and thus that visual attention is not directed on the basis of position information alone.

Adult↗

PubMed1991

Target--distractor separation and feature integration in visual attention to letters.

The interference produced by distractor letters diminishes with increasing distance from a target letter, as if the distractors fall outside an attentional spotlight focussed on the target (Eriksen and Eriksen 1974). We examine Hagenaar and Van der Heijden's (1986) claim that this distance effect is an acuity artefact. Feature integration theory (Treisman 1986) predicts that even when acuity is controlled for, distance effects should be found when interference is produced by conjoined distractor features (e.g. letter-identities), but not when interference arises from isolated distractor features (e.g. letter-strokes). The opposite pattern of results is found. A model is proposed in which both letter-strokes and letter-identities are derived in parallel. The location of letter-strokes can also be coded in parallel, but locating letter-identities may require the operation of attention.

Attention↗

PubMed1989

The role of expression and identity in the face-selective responses of neurons in the temporal visual cortex of the monkey.

Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and the inferior temporal gyrus of macaque monkeys respond to faces. To determine if facial factors such as expression and identity are encoded independently by face-responsive neurons, 45 neurons were tested on a stimulus set depicting 3 monkeys with 3 expressions each. As tested on a two-way ANOVA, 15 neurons showed response differences to different identities independently of expression, and 9 neurons showed responses to different expressions independently of identity. Three neurons showed significant effects of both factors. Six of the neurons with responses related to expression responded primarily to calm faces, while 2 responded primarily to threat faces. Of a further set of 31 neurons tested on pairs of different expressions, 6 showed strong responses to open-mouth fear or threat expressions, while 2 showed stronger responses to calm faces than threat expressions. Neurons responsive to expression were found primarily in the cortex in the superior temporal sulcus, while neurons responsive to identity were found primarily in the inferior temporal gyrus. The difference in anatomical distribution was statistically significant. This supports the possibility that specific impairments of the recognition of the identity of a face and of its expression in man are due to damage to or disconnection of separate neuronal substrates.

Animals↗

PubMed1989

Object-centered encoding by face-selective neurons in the cortex in the superior temporal sulcus of the monkey.

Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and in the inferior temporal cortex respond to faces. To determine if some face responsive neurons encode stimuli in an object-centered coordinate system rather than a viewer-centered coordinate system, a large number of neurons were tested for sensitivity to head movement in 3 macaque monkeys. Ten neurons responded only when a head undergoing rotatory movements was shown. All of these responded to a particular movement independently of the orientation of the moving head in relation to the viewer, maintaining specificity even when the moving head was inverted or shown from the back, thereby reversing viewer-centered movement vectors. This was taken as evidence that the movement was encoded in object-centered coordinates. In tests of whether there are neurons in this area which respond differently to the faces of different individuals relatively independently of viewing angle, it was found that a further 18 neurons responded more to one static face than another across different views. However, for 16 of these 18 cells there was still some modulation of the neuronal response with viewing angle. These 16 neurons thus did not respond perfectly in relation to the object shown independently of viewing angle, and may represent an intermediate stage between a viewer-centered and an object-centered representation. In the same area as these neurons, other cells were found which responded on the basis of viewer-centered coordinates. These neurophysiological findings provide evidence that some neurons in the inferior temporal visual cortex respond to faces (or heads) on the basis of object-centered coordinates, and that others have responses which are intermediate between object-centered and viewer-centered representations. The results are consistent with the hypothesis that object-centered representations are built in the inferior temporal visual cortex.

Animals↗

PubMed1989

The effect of learning on the face selective responses of neurons in the cortex in the superior temporal sulcus of the monkey.

Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and the inferior temporal gyrus of macaque monkeys respond to faces. These neurons provided a consistently identifiable substrate with which studies of the storage of visual information were performed. To determine whether face responsive neurons change how much they respond to different novel faces as they become familiar, neurons were tested with two experimental designs. In the first experiment, 22 neurons were tested on their responsiveness to the different members of a large set of novel faces as the set was presented repeatedly until the faces became familiar. 6 neurons altered the relative degree to which they responded to the different members of the set between the first two presentations and subsequent presentations. In a control condition, only 1 out of 17 neurons showed a significant response difference between the first two presentations and subsequent presentations when the experiment started with faces which were already familiar to the monkey. In the second experiment, 26 neurons were tested on their responsiveness to the different members of a set of familiar faces before and after the addition of a novel face to the set. 5 neurons altered the relative degree in which they responded to the different members of the set of familiar faces after addition of a novel face. It is suggested that these changes in neuronal responsiveness to different stimuli reflect the setting up of an ensemble encoded representation of face stimuli. This alteration of neuronal responsiveness as novel faces become familiar suggests that face responsive neurons may store information useful in visual recognition. In addition to this relatively long-term alteration of relative neuronal responsiveness to different stimuli, it was found that a large number of cells showed a higher mean response to the first presentation of a set of novel faces than to subsequent presentations of the faces. However, the response to the first presentation of a set of familiar faces was also higher than to subsequent presentations in that sequence. This pattern indicates a short term recency effect in the response of these neurons to visual stimuli which is similar to that previously reported (Baylis and Rolls 1987).

Animals↗

PubMed1989

Movement and visual attention: the spotlight metaphor breaks down.

The interfering effects of distractor letters are known to diminish with increasing distance from the target letter (Eriksen & Eriksen, 1974). This result is held to support spotlight models in which visual attention can only be assigned to contiguous regions of the visual field. However, the result is also consistent with the rival claim that attention is assigned to perceptual groups. Four experiments show that grouping of target and distractors by common motion can have more influence than their proximity. Distant distractor letters that move with a target letter produce more interference than static distractors that are nearer the target. Near distractors are equally ineffective if the target is static while they move. These results imply that attention is directed to perceptual groups whose components may be spatially dispersed. The spotlight metaphor seems inappropriate for visual attention in a dynamic environment.

Adult↗

PubMed1989

Individual differences in schizotypy as reflected in measures of cognitive inhibition.

Three experiments are reported using the 'negative priming' paradigm to investigate cognitive differences in normal schizotypal subjects. Lists of Stroop colour words were presented at different display times in a number of priming and non-priming conditions, in one of which the ignored colour name predicted the colour of the next target item. The increased RT latencies to the target normally found in this condition were reduced, or even reversed, in high schizotypal subjects selected on the basis of a new schizotypy scale (STA). This effect was confined to a very short presentation time (100 ms), suggesting that schizotypy is associated with weakened inhibition operating in the early (automatic) stages of information processing. The familiar Stroop (interference) effect was related overall to negative priming, but was not responsible for the schizotypy differences.

Adolescent↗

PubMed1987

Responses of neurons in the inferior temporal cortex in short term and serial recognition memory tasks.

Gaffan and Weiskrantz (1980) and Mishkin (1982) have shown that lesions to the inferior temporal visual cortex can impair the performance of serial visual recognition memory tasks. In order to provide evidence on whether the inferior temporal visual cortex contains a mechanism which enables memory to span the intervening items in a serial recognition task, or whether the inferior temporal cortex is merely afferent to such recent memory mechanisms, we analysed the activity of single neurons in the inferior temporal visual cortex and the adjacent cortex in the superior temporal sulcus in both delayed match to sample and serial recognition memory tasks. In the serial recognition task, various numbers of stimuli intervened between the first and second presentations of a stimulus. A considerable proportion (64/264 or 26%) of visually responsive inferotemporal neurons showed a different response to the "novel" and "familiar" presentations of a stimulus in the serial recognition memory task, and often a corresponding difference in response between the sample and match presentations of a stimulus in the delayed match to sample task. For the majority of neurons this difference was not sustained across even one intervening stimulus in the serial recognition task, and no neurons bridged more than 2 intervening stimuli. These results show that neurons in the inferior temporal cortex have responses which would be useful for a short term visual memory for stimuli, but would not be useful in recency memory tasks in which more than one stimulus intervenes between the first and second presentations of a stimulus. In this investigation, neurons were recorded both in the cortex on the inferior temporal gyrus (commonly called inferior temporal visual cortex, and consisting of areas TE3, TE2 and TE1 of Seltzer and Pandya 1978), and in the cortex in the adjacent anterior part of the superior temporal sulcus, in which a number of different temporal cortical visual areas have now been described.

Animals↗

PubMed1987

The responses of neurons in the cortex in the superior temporal sulcus of the monkey to band-pass spatial frequency filtered faces.

There are neurons in the cortex in the anterior part of the superior temporal sulcus of the macaque monkey with visual responses which would be useful for face recognition (Rolls, 1984; Baylis et al., 1985). To analyze further the information which leads them to respond, their responses were measured to parametrically filtered stimuli. The responses of 48 such single neurons were measured to faces which were digitized and were bandpass spatial frequency filtered. The octave width bands were 2-4, 4-8, 8-16, 16-32, 32-64 and 64-128 cycles per image. It was found that the neurons could respond well to single octaves of the spatial frequencies normally present in faces, that the most effective bands were 4-8, 8-16 and 16-32 cycles per face (cpf), and that the bands 2-4 and 32-64 cpf were partly effective. In investigations of whether the responses of the neurons to an unfiltered face, and to low-pass and high-pass filtered images could be predicted by linear addition of their responses to each of the octave bands shown separately, it was found that the majority of the neurons were non-linear, and responded much less than predicted. It was also shown that this occurred even when the contrast was reduced to 0.25 of that normally present in a face, so that the result was not due just to a ceiling effect of the maximum firing rate. These results help to define parametrically the aspects of the information normally present in a face which are sufficient to produce responses of these neurons to them, and show that linear operations cannot account for information processing in this part of the visual system.

Action Potentials↗

PubMed1987

Functional subdivisions of the temporal lobe neocortex.

In order to gather evidence on functional subdivisions of the temporal lobe neocortex of the primate, the activity of more than 2600 single neurons was recorded in 10 myelo- and cytoarchitecturally defined subdivisions of the cortex in the superior temporal sulcus (STS) and inferior temporal gyrus of the anterior part of the temporal lobe of 5 hemispheres of 3 macaque monkeys. First, convergence of different modalities into each area was investigated. Areas TS and TAa, in the upper part of this region, were found to receive visual as well as auditory inputs. Areas TPO, PGa, and IPa, in the depths of the STS, received visual, auditory, and somatosensory inputs. Areas TEa, TEm, TE3, TE2, and TE1, which extend from the ventral bank of the STS through the inferior temporal gyrus, were primarily unimodal visual areas. Second, of the cells with visual responses, it was found that some neurons in areas TS-IPa could be activated only by moving visual stimuli, whereas the great majority of neurons in areas TEa-TE1 could be activated by stationary visual stimuli. Third, it was found that there were few sharply discriminating visual neurons in areas TS and TAa; of the sharply discriminating visual neurons in other areas, however, neurons that responded primarily to faces were found predominantly in areas TPO, TEa, and TEm (in which they represented 20% of the neurons with visual responses); neurons that were tuned to relatively simple visual stimuli such as sine-wave gratings, color, or simple shapes were relatively common in areas TEa, TEm, and TE3; and neurons that responded only to complex visual stimuli were common in areas IPa, TEa, TEm, and TE3. These findings show inter alia that areas TPO, PGa, and IPa are multimodal, that the inferior temporal gyrus areas are primarily unimodal, that there are areas in the cortex in the anterior and dorsal part of the STS that are specialized for the analysis of moving visual stimuli, that neurons responsive primarily to faces are found predominantly in areas TPO, TEa, and TEm, and that architectural subdivisions of the temporal lobe cortex are related to neuronal response properties.

Action Potentials↗

PubMed1986

Size and contrast have only small effects on the responses to faces of neurons in the cortex of the superior temporal sulcus of the monkey.

There is a population of neurons in the cortex in the middle and anterior part of the superior temporal sulcus (STS) of the monkey with responses which are selective for faces. To investigate whether the responses of these neurons show some of the perceptual properties of face recognition such as tolerance to changes in the size and contrast of the face, the effects of alteration of the size and contrast of an effective face stimulus on the responses of these neurons were analysed quantitatively in macaque monkeys. First, it was shown that the majority of these neurons had responses which were relatively invariant with respect to the size of the stimulus. The median size change tolerated with a response of greater than half the maximal response was 12 times. Second, it was found that for a few of these neurons, the size of the face did affect the neuronal response. For most of these neurons, it was found that when the size of the image and its distance were altered, the neuronal response was related to the retinal angle subtended by the image. But for four neurons the absolute size of the image determined the magnitude of the neuronal response, independently of the distance of the image. Thus these four neurons showed size constancy. It is suggested that these neurons would be useful as part of a face recognition system, because only objects in a certain absolute size range should normally be classified as faces. Third, the responses of the neurons were relatively invariant with respect to the contrast of the face. The mean contrast at which the neurons still responded with more than half the maximal response was 0.26. Fourth, the responses of the neurons were relatively invariant with respect to the sign of the contrast of the face, that is the neurons responded to negative as well as to positive images of faces. Fifth, the neurons typically responded to a face when the information in it had been reduced from 3D to a 2D representation in gray on a monitor, with a response which was on average 0.5 that to a real face. These results show that the responses of these neurons have some of the invariant properties with respect to size and contrast alteration shown by face perception, and show that their processing is at a level which would be useful in face recognition.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1985

Selectivity between faces in the responses of a population of neurons in the cortex in the superior temporal sulcus of the monkey.

There is a population of neurons in the cortex in the middle and anterior part of the superior temporal sulcus (STS) of the monkey with responses which are selective for faces. If, consistent with the effects of damage to the temporal lobe, these neurons are involved in face recognition or in making appropriate social responses to different individuals, then it might be expected that at least some of these neurons might respond differently to different faces. To investigate whether at least some of these neurons do respond differently to different faces, their responses were measured to a standard set of faces, presented in random sequence using a video framestore. It was found that a considerable proportion of the neurons with face-selective responses tested (34/44 or 77%) responded differently to different faces, as shown by analyses of variance. An index of the discriminability of the most and least effective face stimulus (d') ranged between 0.2 and 5.0 for the different neurons. Although these neurons often responded differently to different faces, they did not usually respond to only one of the faces in the set, so that information that a particular face had been shown was present across an ensemble of neurons, rather than in the responses of an individual neuron. These findings indicate that the responses of these neurons would be useful in providing information on which different behavioral responses made to different faces could be based. These neurons could thus be filters, the output of which could be used for recognition of different individuals and in emotional responses made to different individuals.

Animals↗

PubMed1985

Role of low and high spatial frequencies in the face-selective responses of neurons in the cortex in the superior temporal sulcus in the monkey.

There are neurons in the cortex in the anterior part of the superior temporal sulcus of the macaque monkey with visual responses selective for faces. One aim of the present study was to analyze further the information which leads them to respond, by measuring their responses to parametrically filtered stimuli. The responses of 32 such single neurons were measured to faces which were digitized, lowpass filtered at spatial frequencies of 2, 4, 8,...128 cycles/face, highpass filtered at frequencies of 4, 8,...64 cycles/face, and presented in random sequence using a video framestore. It was found that many of the neurons could respond to blurred images of faces, with a mean frequency at half-maximum amplitude of the neuronal response to the series of lowpass filtered images of faces of 3.3 cycles/face. Almost all the neurons had lowpass cutoff frequencies defined in this way below 8 cycles/face. Many of the neurons could also respond to images of faces in which the only information remaining was a limited amount of high spatial frequency edge information. The mean frequency at half-maximum amplitude of the neuronal response to the series of highpass filtered images of faces was 29.7 cycles/face. Almost all the neurons had highpass cutoff frequencies above 8 cycles/face. Thus, many of the neurons could respond to a lowpass and a highpass filtered image of a face even when these had no spatial frequencies in common. The mean separation between the lowpass and highpass cutoff frequencies was 3.2 octaves. For comparison, face recognition in man can be performed with images which contain only information up to 8 cycles/face, or with highpass filtered images which contain only information down to 8 cycles/face. The response of the neurons was not always a smooth function of frequency, but could decrease as higher frequencies were included in the lowpass filtered images of faces, or as low frequencies were included in the highpass filtered images of faces. This indicates that information in certain frequency bands was able to inhibit these neurons. This was particularly likely to occur for the non-optimal face stimulus for a given neuron, indicating that the selectivity of these neurons to different faces was a combination of the excitation produced by some information in faces and inhibition produced by other.

Action Potentials↗

PubMed1985

Neurons in the amygdala of the monkey with responses selective for faces.

To investigate the functions of the amygdala in visual information processing and in emotional and social responses, recordings were made from single neurons in the amygdala of the monkey. A population of neurons (40 of more than 1000 recorded in 4 monkeys) was investigated which responded primarily to faces. These neurons typically (1) responded to some human or monkey faces, which were presented to the monkey through a large aperture shutter so that response latencies could be measured, or were simply shown to the monkey, (2) responded to 2-dimensional representations of these faces, as well as to real 3-dimensional faces, (3) had no responses or only small (less than half maximum) responses to gratings, simple geometrical, other complex 3-D stimuli, or to arousing and aversive stimuli, (4) had response latencies of 110-200 ms, (5) were located in the basal accessory nucleus of the amygdala, (6) responded differently to different faces, as shown by measures of d', and could thus over a population of such neurons code information useful for making different responses to different individuals, (7) could in some cases (9/11 tested) respond to parts of faces, and (8) in a few cases (4/19 tested) responded more to a face which produced an emotional response. A comparison made in three monkeys of the responses of these neurons with the responses of 77 neurons with face-selective responses recorded in the cortex of the superior temporal sulcus (STS) showed that the amygdaloid neurons had longer response latencies (110-200 compared to 90-140 ms), and were in some respects more selective in their responses to different faces. It is suggested that the deficits in social and emotional behavior produced by amygdala lesions could be due in part to damage to a neuronal system specialized in utilizing information from faces so that appropriate social and emotional responses can be made to different individuals.

Amygdala↗

PubMedDate not supplied

Deficits of motor intention following parietal lesions.

Patients with lesions to the right parietal lobe were tested on their ability to reach to targets, or to respond verbally to targets. The targets occurred at the same two spatial locations--to the left and right of the patient--with the task being cued by the color of the target. Patients were able to perform both tasks separately rapidly and without error. However, when the two tasks were interleaved, they had difficulty making a response in the left (contralesional) field when this was different to a response that they had just made. These results suggest that lesions to the parietal cortex may cause a deficit in the coding for motor intention, as well as attention in the contralesional field.

Aged↗