- Email: [email protected]
Reaching for the parietal cortex
Update Monitor
On agents and actions
Just an illusion
Human social cognition relies to some degree on the ability to attribute actions to their proper agents and the ability to understand the meaning of actions when they are performed by others. Some of the symptoms of psychiatric diseases such as schizophrenia have been suggested to result from an impaired awareness of one’s own actions and to a disrupted ability to recognize the actions of others. It therefore follows that studying the performance of these patient groups may lead to a greater understanding of agency – the attribution of actions. Daprati et al. studied the ability of schizophrenic subjects, with and without delusion of control, to perform simple finger and wrist movements in the absence of direct visual control of their hand. Using a sophisticated video and mirror arrangement, subjects were shown a real-time image of either their own gloved hand performing the movement, or an alien gloved
While memory systems often work effectively to produce an accurate representation of the past, there are occasions when memory can be distorted and errors can occur in both recall and recognition. This has been successfully demonstrated using a paradigm in which the subject is presented with a series of lists, each of which is composed of words that are associated with a single ‘theme word’ that is never presented. For example, sour, sugar, candy, sugar, bitter and good form a list of words that are associated with the ‘theme word’ sweet. When asked to recall the words in the list subjects frequently introduce the ‘theme word’ which was, in fact, never presented. A ‘remember’/’know’ modification of the basic task, in which the subjects were asked to indicate if they consciously recollected specific details of the presentation of the word during the study list, revealed that they frequently claim to recollect having heard the ‘theme word’. Norman and Schacter have now investigated the source of this illusory recollection. Asking the subjects to write down exactly what they remembered about the presentation of the falsely recollected ‘theme word’ had no effect on the rate of false recollections – indicting that the subjects were recollecting specific information (albeit illusory) rather than misappropriating a strong feeling of familiarity. A subsequent experiment in which focused questions were used to probe the source of this information suggested that both veridical and illusory memories were mostly composed of associative information (memory for words and thoughts associated with the target word) rather than sensory or contextual detail (sound, list position and reaction). These results therefore provide an important advance in our understanding of false memories.
hand performing either the same movement or a different movement. The subjects’ task was to discriminate their own hand movement. The results indicated that the delusional and hallucinating schizophrenic subjects were less able to discriminate their own hand from alien hands when compared with non-hallucinating subjects. They also had a tendency to attribute mistakenly an alien hand as their own. These results are consistent with reports that hallucinating subjects are likely to incorporate external events into their perception of their own experience, and are discussed in the context of the cues that are used to produce conscious judgements regarding the origin of actions. Reference Daprati, E. et al. (1997) Looking for the agent: an investigation into consciousness of action and self-consciousness
in
schizophrenic
patients
Cognition 65, 71–86
Mirror, mirror on the wall Learning to read words that are presented in a mirror, and are therefore reversed by the mirror, is a time consuming business that requires a lot of practice. Neuropsychological evidence indicates that the neural substrate underlying this perceptual skill probably includes the basal ganglia rather than the medial temporal lobe, diencephalic structures and the cerebellum, because patients with Huntington’s disease are impaired while patients with amnesia or cerebellar damage are not. Poldrack et al. now report the results of a functional magnetic resonance imaging (fMRI) study that demonstrates the altered neural activity that are associated with the acquisition of mirror-reading skill for novel or practised words. When reading mirrorreversed text was compared with read-
ing normally oriented text, the activity in multiple regions in the occipital lobe, inferior temporal cortex, superior parietal cortex and cerebellum was modulated. Skilled mirror reading of novel stimuli was associated with decreased activation in the right superior parietal cortex and posterior occipital cortex and an increased activation in the left inferior temporal areas. These results are interpreted as evidence for a progression from visuospatial transformation to direct recognition of the mirror-reversed letters, consistent with a processswitching account of skill learning.
Reference Reference
Norman, K.A. and Schacter, D.L. (1997) False
Poldrack, R.A. et al. (1998) The neural basis of
recognition
visual skill learning: An fMRI study of mirror
Exploring the characteristics of illusory memories
reading Cereb. Cortex 8, 1–10
Mem. Cognit. 26, 838–848
Reaching for the parietal cortex During reaching movements, sensory signals must be transformed into an appropriate set of motor commands. For visually guided movements, this will involve transforming visual information signalling the spatial position of the target, into a motor plan specifying the sequence of postural changes required to bring the hand to the target. A longstanding issue within motor control research has therefore been to determine whether reaching movements are planned primarily in extrinsic (spatial) or intrinsic (body) coordinates1. A recent study carried out by Rushworth and
colleagues has thrown new light on this issue; suggesting that visually guided and proprioceptively guided reaching movements may be mediated by separate regions of the parietal lobe2. Rushworth and colleagues examined the effects of bilateral parietal lesions on the reaching movements of non-human primates. Reaching movements were either directed to visually defined targets, or executed in the dark to target locations defined with reference to proprioceptive cues. The results of the study demonstrated that bilateral lesions of Brodmann’s areas 7a, 7ab, and the adjacent
in
younger
and
older
adults:
lateral bank of the intraparietal sulcus (putative ‘visuomotor’ regions) produced reaching impairments on visually guided reaches but not during proprioceptively guided reaches. In contrast, bilateral lesions to Brodmann’s areas 7b, 5, and the adjacent medial bank of the intraparietal sulcus (putative ‘somatomotor’ regions) produced reaching impairments on proprioceptively guided reaches but not during visually guided reaches. References 1 Georgopoulos, A.P. (1995) Trends Neurosci. 18, 506–510, 2 Rushworth,
M.F.S.,
Nixon,
P.D.,
and
Passingham, R.E. (1997) Exp. Brain Res. 117, 292–310
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 1364-6613/98/$19.00 Trends in Cognitive Sciences – Vol. 2, No. 3,
March 1998
81
On agents and actions
Just an illusion
Human social cognition relies to some degree on the ability to attribute actions to their proper agents and the ability to understand the meaning of actions when they are performed by others. Some of the symptoms of psychiatric diseases such as schizophrenia have been suggested to result from an impaired awareness of one’s own actions and to a disrupted ability to recognize the actions of others. It therefore follows that studying the performance of these patient groups may lead to a greater understanding of agency – the attribution of actions. Daprati et al. studied the ability of schizophrenic subjects, with and without delusion of control, to perform simple finger and wrist movements in the absence of direct visual control of their hand. Using a sophisticated video and mirror arrangement, subjects were shown a real-time image of either their own gloved hand performing the movement, or an alien gloved
While memory systems often work effectively to produce an accurate representation of the past, there are occasions when memory can be distorted and errors can occur in both recall and recognition. This has been successfully demonstrated using a paradigm in which the subject is presented with a series of lists, each of which is composed of words that are associated with a single ‘theme word’ that is never presented. For example, sour, sugar, candy, sugar, bitter and good form a list of words that are associated with the ‘theme word’ sweet. When asked to recall the words in the list subjects frequently introduce the ‘theme word’ which was, in fact, never presented. A ‘remember’/’know’ modification of the basic task, in which the subjects were asked to indicate if they consciously recollected specific details of the presentation of the word during the study list, revealed that they frequently claim to recollect having heard the ‘theme word’. Norman and Schacter have now investigated the source of this illusory recollection. Asking the subjects to write down exactly what they remembered about the presentation of the falsely recollected ‘theme word’ had no effect on the rate of false recollections – indicting that the subjects were recollecting specific information (albeit illusory) rather than misappropriating a strong feeling of familiarity. A subsequent experiment in which focused questions were used to probe the source of this information suggested that both veridical and illusory memories were mostly composed of associative information (memory for words and thoughts associated with the target word) rather than sensory or contextual detail (sound, list position and reaction). These results therefore provide an important advance in our understanding of false memories.
hand performing either the same movement or a different movement. The subjects’ task was to discriminate their own hand movement. The results indicated that the delusional and hallucinating schizophrenic subjects were less able to discriminate their own hand from alien hands when compared with non-hallucinating subjects. They also had a tendency to attribute mistakenly an alien hand as their own. These results are consistent with reports that hallucinating subjects are likely to incorporate external events into their perception of their own experience, and are discussed in the context of the cues that are used to produce conscious judgements regarding the origin of actions. Reference Daprati, E. et al. (1997) Looking for the agent: an investigation into consciousness of action and self-consciousness
in
schizophrenic
patients
Cognition 65, 71–86
Mirror, mirror on the wall Learning to read words that are presented in a mirror, and are therefore reversed by the mirror, is a time consuming business that requires a lot of practice. Neuropsychological evidence indicates that the neural substrate underlying this perceptual skill probably includes the basal ganglia rather than the medial temporal lobe, diencephalic structures and the cerebellum, because patients with Huntington’s disease are impaired while patients with amnesia or cerebellar damage are not. Poldrack et al. now report the results of a functional magnetic resonance imaging (fMRI) study that demonstrates the altered neural activity that are associated with the acquisition of mirror-reading skill for novel or practised words. When reading mirrorreversed text was compared with read-
ing normally oriented text, the activity in multiple regions in the occipital lobe, inferior temporal cortex, superior parietal cortex and cerebellum was modulated. Skilled mirror reading of novel stimuli was associated with decreased activation in the right superior parietal cortex and posterior occipital cortex and an increased activation in the left inferior temporal areas. These results are interpreted as evidence for a progression from visuospatial transformation to direct recognition of the mirror-reversed letters, consistent with a processswitching account of skill learning.
Reference Reference
Norman, K.A. and Schacter, D.L. (1997) False
Poldrack, R.A. et al. (1998) The neural basis of
recognition
visual skill learning: An fMRI study of mirror
Exploring the characteristics of illusory memories
reading Cereb. Cortex 8, 1–10
Mem. Cognit. 26, 838–848
Reaching for the parietal cortex During reaching movements, sensory signals must be transformed into an appropriate set of motor commands. For visually guided movements, this will involve transforming visual information signalling the spatial position of the target, into a motor plan specifying the sequence of postural changes required to bring the hand to the target. A longstanding issue within motor control research has therefore been to determine whether reaching movements are planned primarily in extrinsic (spatial) or intrinsic (body) coordinates1. A recent study carried out by Rushworth and
colleagues has thrown new light on this issue; suggesting that visually guided and proprioceptively guided reaching movements may be mediated by separate regions of the parietal lobe2. Rushworth and colleagues examined the effects of bilateral parietal lesions on the reaching movements of non-human primates. Reaching movements were either directed to visually defined targets, or executed in the dark to target locations defined with reference to proprioceptive cues. The results of the study demonstrated that bilateral lesions of Brodmann’s areas 7a, 7ab, and the adjacent
in
younger
and
older
adults:
lateral bank of the intraparietal sulcus (putative ‘visuomotor’ regions) produced reaching impairments on visually guided reaches but not during proprioceptively guided reaches. In contrast, bilateral lesions to Brodmann’s areas 7b, 5, and the adjacent medial bank of the intraparietal sulcus (putative ‘somatomotor’ regions) produced reaching impairments on proprioceptively guided reaches but not during visually guided reaches. References 1 Georgopoulos, A.P. (1995) Trends Neurosci. 18, 506–510, 2 Rushworth,
M.F.S.,
Nixon,
P.D.,
and
Passingham, R.E. (1997) Exp. Brain Res. 117, 292–310
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 1364-6613/98/$19.00 Trends in Cognitive Sciences – Vol. 2, No. 3,
March 1998
81