- Email: [email protected]
Modeling line bisection
Visually
guided
Effective control of visually guided reaching movements necessitates a functional mapping between the seen and felt positions of the hand. This can be easily demonstrated by dissociating visual and proprioceptive inputs, such as when reaching wearing displacing prisms. In such circumstances however, the visuomotor systems shows a high degree of flexibility, rapidly adapting to prismatic displacement by re-aligning the proprioceptive map. Clower and
reaching
colleagues recently carried out a functional brain-imaging study using positron emission tomography to identify brain regions associated with prism adaptation. In their study, subjects were scanned during reaching while wearing displacing prisms, and also while they performed an error-correction task (reaching for a target which was randomly displaced during mid-reach). A Comparison between these conditions revealed an area of increased activation
How do we recognize speech? In order to recognize speech from other sounds in the environment we are required to perceive changes in the sound spectrum that occur over tens of milliseconds. This positron emission tomography study was designed to determine whether the known left-hemisphere specialization for language might be based in part on a relative specialization of this hemisphere for the processing of such rapid changes. Subjects were scanned while discriminating pure-tone stimuli incorporating frequency glides of either short or long duration. Relative to the long-glide condition, short-glide dis-
Modeling
crimination yielded changes in cerebral blood flow that were mainly located in the left hemisphere. Because nonlinguistic stimuli were used, Johnsrude et a/. were able to conclude that this asymmetric activation reflects a general specialization of the human left hemisphere for the processing of shortduration spectral changes and this could be relevant to speech perception. Reference
Johnsrude. IS. et al. (1997) Left-hemisphere specialization for the processing of acoustic transients NeuroReport7, 1761-1765
line bisection
Unilateral neglect is a clinical syndrome which commonly results from lesions to the right hemisphere and manifests as a failure to explore, orient or respond to, stimuli located within contralateral space. When required to mark the centre of a horizontal line, patients with unilateral neglect frequently transect the line to the right of centre. Mozer et a/. demonstrate that an existing computational model of visual perception and selective attention (MORSEL) successfully simulated most aspects of the performance of neglect patients on a series of line bisection tasks, when the
attentional mechanism of the model was ‘lesioned’. This report is intriguing because the model and the ‘lesion’ were not specifically designed to account for the line bisection data. In addition, the authors speculate that the model predicts that under some circumstances brief, masked stimulus presentations may alleviate the symptoms of neglect.
Read my lips
auditory association cortex) which are also active during auditory speech processing. Subsequent experiments demonstrated that these auditory areas were not activated by silent viewing of non-linguistic facial movements, but were engaged during silent meaningless speech movements (pseudospeech). This study therefore provides the first demonstration of the brain areas involved in the integration of information from visual and auditory modalities and suggest that lipreading modulates speech perception at a pre-lexical level.
The influence of visual cues on auditory speech perception can be both positive and negative. Thus, speech perception is improved in noisy surroundings by the visual cues provided by watching the speakers lips, but can be disrupted if the speakers lips do not move in synchrony with the heard speech. The latter case is a common problem with poorly dubbed films. Calvet-t et a/., using functional magnetic resonance imaging, provide compelling evidence that silent lipreading in the absence of speech sounds activated lateral areas of the temporal auditory cortex (primary auditory and
Reference
Mozer, M.C., Halligan, P.W. and Marshall, J.C. (1997) The end of the line for a brain-damaged model of unilateral neglect 1. Cogn. Neurosci. 2, 171-190
I”
Cognltlve
Sciences
- Vol.
Reference
Glower. D.M. et al. (1996) Role of posterior parietal cortex in the recalibration of visually guided reaching Nature 383, 618-621
Travelling salesman problem: a foot-in-the-door? Planning the optimal route between a given number of locations is a complex cognitive process that has been studied widely as the ‘travelling salesman problem’. Cramer and Gallistel examined the ability of vervet monkeys (cercopithecus to forage for food in an oraethiops) dered manner by carrying them around an enclosure so that the monkeys could observe them hiding food in up to eight small holes that had been selected randomly from an array of 25 possible locations. The monkeys largely ignored the order in which the locations were baited and tended to minimize the distance travelled, although the number of sites visited was much less than that seen with chimpanzees in earlier experiments. Interestingly, two additional experiments suggest that the vervet monkeys did not simply move from one location to the next nearest neighbour. Rather the monkeys seemed to take into account up to two future destinations when selecting each move. If the array of hiding places formed a ‘diamond’ shape and the monkeys were not required to return to the starting position, the optimal search path (both mid-locations, then far end location) was used on the majority of searches. However, if the monkeys were required to return to the starting position, they used a different route (mid-location, far end, mid location, start) but again minimized the distance travelled. Furthermore, if the monkeys were an equal distance from a group of two locations on one side of the enclosure and a group of four locations on the other side of the enclosure, they always visited the side with four locations first, so maximizing the reward early in the search. One explanation for both results is that the monkeys take into account more than one future destination when planning a route. If so these data provide an intriguing glimpse of the planning abilities of monkeys.
Reference Calvert, G.A. et al. (1997) Activation of auditory cortex during silent lipreading Science 276, 593496
Copyright @ 1997, Elsevier Science Ltd. All rights reserved. 1364-6613/97/$17.00 Trends
in the lateral bank of the contralateral intraparietal sulcus (area PEG) associated with the prism adaptation task. It is of interest to note that neurophysiological studies of this brain region in the monkey (area VIP) reveal the existence of bimodal (visuallsomatosensory) cells in which the visual and somatosensory receptive fields are aligned with one another.
1, No.
4.
July
1997
Reference
Cramer, A.E. and Gallistel, C.R. (1997) Vervet monkeys as travelling salesmen Nature 387. 464
guided
Effective control of visually guided reaching movements necessitates a functional mapping between the seen and felt positions of the hand. This can be easily demonstrated by dissociating visual and proprioceptive inputs, such as when reaching wearing displacing prisms. In such circumstances however, the visuomotor systems shows a high degree of flexibility, rapidly adapting to prismatic displacement by re-aligning the proprioceptive map. Clower and
reaching
colleagues recently carried out a functional brain-imaging study using positron emission tomography to identify brain regions associated with prism adaptation. In their study, subjects were scanned during reaching while wearing displacing prisms, and also while they performed an error-correction task (reaching for a target which was randomly displaced during mid-reach). A Comparison between these conditions revealed an area of increased activation
How do we recognize speech? In order to recognize speech from other sounds in the environment we are required to perceive changes in the sound spectrum that occur over tens of milliseconds. This positron emission tomography study was designed to determine whether the known left-hemisphere specialization for language might be based in part on a relative specialization of this hemisphere for the processing of such rapid changes. Subjects were scanned while discriminating pure-tone stimuli incorporating frequency glides of either short or long duration. Relative to the long-glide condition, short-glide dis-
Modeling
crimination yielded changes in cerebral blood flow that were mainly located in the left hemisphere. Because nonlinguistic stimuli were used, Johnsrude et a/. were able to conclude that this asymmetric activation reflects a general specialization of the human left hemisphere for the processing of shortduration spectral changes and this could be relevant to speech perception. Reference
Johnsrude. IS. et al. (1997) Left-hemisphere specialization for the processing of acoustic transients NeuroReport7, 1761-1765
line bisection
Unilateral neglect is a clinical syndrome which commonly results from lesions to the right hemisphere and manifests as a failure to explore, orient or respond to, stimuli located within contralateral space. When required to mark the centre of a horizontal line, patients with unilateral neglect frequently transect the line to the right of centre. Mozer et a/. demonstrate that an existing computational model of visual perception and selective attention (MORSEL) successfully simulated most aspects of the performance of neglect patients on a series of line bisection tasks, when the
attentional mechanism of the model was ‘lesioned’. This report is intriguing because the model and the ‘lesion’ were not specifically designed to account for the line bisection data. In addition, the authors speculate that the model predicts that under some circumstances brief, masked stimulus presentations may alleviate the symptoms of neglect.
Read my lips
auditory association cortex) which are also active during auditory speech processing. Subsequent experiments demonstrated that these auditory areas were not activated by silent viewing of non-linguistic facial movements, but were engaged during silent meaningless speech movements (pseudospeech). This study therefore provides the first demonstration of the brain areas involved in the integration of information from visual and auditory modalities and suggest that lipreading modulates speech perception at a pre-lexical level.
The influence of visual cues on auditory speech perception can be both positive and negative. Thus, speech perception is improved in noisy surroundings by the visual cues provided by watching the speakers lips, but can be disrupted if the speakers lips do not move in synchrony with the heard speech. The latter case is a common problem with poorly dubbed films. Calvet-t et a/., using functional magnetic resonance imaging, provide compelling evidence that silent lipreading in the absence of speech sounds activated lateral areas of the temporal auditory cortex (primary auditory and
Reference
Mozer, M.C., Halligan, P.W. and Marshall, J.C. (1997) The end of the line for a brain-damaged model of unilateral neglect 1. Cogn. Neurosci. 2, 171-190
I”
Cognltlve
Sciences
- Vol.
Reference
Glower. D.M. et al. (1996) Role of posterior parietal cortex in the recalibration of visually guided reaching Nature 383, 618-621
Travelling salesman problem: a foot-in-the-door? Planning the optimal route between a given number of locations is a complex cognitive process that has been studied widely as the ‘travelling salesman problem’. Cramer and Gallistel examined the ability of vervet monkeys (cercopithecus to forage for food in an oraethiops) dered manner by carrying them around an enclosure so that the monkeys could observe them hiding food in up to eight small holes that had been selected randomly from an array of 25 possible locations. The monkeys largely ignored the order in which the locations were baited and tended to minimize the distance travelled, although the number of sites visited was much less than that seen with chimpanzees in earlier experiments. Interestingly, two additional experiments suggest that the vervet monkeys did not simply move from one location to the next nearest neighbour. Rather the monkeys seemed to take into account up to two future destinations when selecting each move. If the array of hiding places formed a ‘diamond’ shape and the monkeys were not required to return to the starting position, the optimal search path (both mid-locations, then far end location) was used on the majority of searches. However, if the monkeys were required to return to the starting position, they used a different route (mid-location, far end, mid location, start) but again minimized the distance travelled. Furthermore, if the monkeys were an equal distance from a group of two locations on one side of the enclosure and a group of four locations on the other side of the enclosure, they always visited the side with four locations first, so maximizing the reward early in the search. One explanation for both results is that the monkeys take into account more than one future destination when planning a route. If so these data provide an intriguing glimpse of the planning abilities of monkeys.
Reference Calvert, G.A. et al. (1997) Activation of auditory cortex during silent lipreading Science 276, 593496
Copyright @ 1997, Elsevier Science Ltd. All rights reserved. 1364-6613/97/$17.00 Trends
in the lateral bank of the contralateral intraparietal sulcus (area PEG) associated with the prism adaptation task. It is of interest to note that neurophysiological studies of this brain region in the monkey (area VIP) reveal the existence of bimodal (visuallsomatosensory) cells in which the visual and somatosensory receptive fields are aligned with one another.
1, No.
4.
July
1997
Reference
Cramer, A.E. and Gallistel, C.R. (1997) Vervet monkeys as travelling salesmen Nature 387. 464