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TRENDS in Cognitive Sciences Vol.5 No.6 June 2001
233
In Brief
Cognitive science fiction Cognitive science looks more like science fiction in a US lab where scientists are working on a new generation of cyborg. Half-fish, half-robot, their creation is capable of responding to light. The researchers connect the brainstem of a lamprey to a small robot on wheels, tapping into the neural network normally responsible for the lamprey’s orienting reflex. When the robot detects light, it sends an electrical signal to the disembodied brain, and the brain responds by sending a signal to the wheels, causing cyborg to move towards or away from the light source. As Sandro Musso-Ivaldi, at Northwestern University, explained to TICS, ‘the robot generates stimuli for the vestibular nerves of the lamprey and receives motor commands from the reticular neurons. The final outcome is a sensory–motor behavior of the robot, organized by the connections in the lamprey’s brain’. The team hope to use their neuro-robotic system to find out about the computational properties of synaptic plasticity. Such advances in cybernetics should also speed the development of brain-controlled prostheses.
Stimulating feedback A new study reveals the importance of feedback connections for human visual awareness [Pascual-Leone, A. and Walsh, V. (2001) Science 292, 510–512]. The researchers used transcranial magnetic stimulation (TMS) to excite primary visual cortex, V1, and the visual motion area, V5. This allowed them to work out the relative timing of events in the two areas. Stimulation of visual areas evokes ‘phosphenes’, or unstructured visual sensations. V5 was stimulated above the threshold for phosphenes, and V1 below threshold. V5 stimulation thereby evoked moving phosphenes, whereas V1 stimulation acted as a temporary lesion by introducing local electrical noise. Disrupting V1 activity before V5 stimulation had no effect on the perception of visual motion. However, disrupting V1 activity 5–45 ms after V5 stimulation abolished or reduced the sensation of visual motion. Walsh commented, ‘the work follows earlier TMS studies of blind and blindsighted patients by myself and Cowey, which showed that V5
phosphenes could not be elicited in the absence of V1.’ The study also highlights the strength of TMS as a technique for determining the timing of neural events, as it provides an estimate of the time for signals to travel from one cortical region to another. HJB
James or Jane? Several studies presented at the Vision Sciences Society Conference (Sarasota, USA, May 2001) revealed new findings on how we use vision to judge gender. Michael J. Tarr and his colleagues showed that, because of the reflectance properties of hair and skin, adult faces differ in colour according to gender, with male faces containing relatively more red and female faces more green. An optimal model using colour alone can discriminate the gender of a face with 75% accuracy. Presenting extremely blurred faces, Tarr et al. found that human subjects can also perform rapid sex classification of faces using colour. Also, Ian Thornton and co-workers used ‘point walker’ displays, in which only the motion of several points on the human body is visible, to study how we perceive gender from information about gait. Both men and women, who had to search for male or female walkers from amongst figures of the other sex, were quicker at the search task when the target was of the opposite sex from that of the subject. MW
Animal concepts Animals may possess much more complex concepts that previously thought, and even a form of consciousness, two recent studies report. The honeybee can perform a ‘delayed match-to-sample’ task: when exposed to the color red and later given the choice between red and green, the insect can be trained to choose red. In a recent report, Martin Giurfa and co-workers (Nature 410, 930-933) report that honeybees trained in this way can generalize correctly to previously unseen stimuli, even when in other modalities, and so can be shown to learn and use the abstract concept of ‘same’ (and ‘different’). For instance, when first trained to choose the same color, the insect generalizes and chooses the same shape, or the same smell. In another recent study (Proc. Natl. Acad. Sci. U. S. A. 98, 5359–5362), Robert R.
Hampton suggests that monkeys might possess a form of introspective consciousness previously thought to be unique to humans, namely the knowledge of whether we remember. For instance, says Hampton, we know whether we remember someone’s phone number or not, without having to place a call to test our memory. Monkeys, when given a chance to take a memory test for a reward, or to decline the test but receive a smaller reward, are more likely to decline when their memory is less reliable – showing that the animals have access to their own mental states. MW
It’s not what you look at, it’s what you see New research is showing that the brain reacts not only to a sensory stimulus, but to how, or whether, the stimulus is actually perceived. Studying how monkeys react to hard-to-detect visual stimuli, Hans Supèr and his colleagues (Nat. Neurosci. 4, 304–310) have shown that even neurons in the primary visual cortex are sensitive to the stimulus-perception difference. Although the visual stimulus remains the same, some neurons respond differently depending on whether the stimulus is detected or missed. Another study on monkeys, presented by Ziv Williams and co-workers at the Vision Sciences Society Conference (Sarasota, USA, May 2001), examined the response of neurons in the parietal cortex to ambiguous apparent-motion displays (such as the flashing lights around the edges of signs). After watching the motion, the monkeys indicated the direction in which they perceived it to move. Whereas the stimulus itself was totally ambiguous, Williams et al. found that the discharge of some parietal neurons was correlated with the subjectively perceived direction of motion. MW
Visual illusions and prefrontal cortex A new study demonstrates that prefrontal cortex activity can reflect the perception of a visual illusion [Lebedev, M.A. et al. (2001) J. Neurophysiol. 85, 1395–1411]. The researchers trained a monkey to fixate a spot of light surrounded by a frame of other lights. The lights disappeared and then reappeared, sometimes in a new location. The monkey had to decide whether the spot
http://tics.trends.com 1364-6613/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
TRENDS in Cognitive Sciences Vol.5 No.6 June 2001
233
In Brief
Cognitive science fiction Cognitive science looks more like science fiction in a US lab where scientists are working on a new generation of cyborg. Half-fish, half-robot, their creation is capable of responding to light. The researchers connect the brainstem of a lamprey to a small robot on wheels, tapping into the neural network normally responsible for the lamprey’s orienting reflex. When the robot detects light, it sends an electrical signal to the disembodied brain, and the brain responds by sending a signal to the wheels, causing cyborg to move towards or away from the light source. As Sandro Musso-Ivaldi, at Northwestern University, explained to TICS, ‘the robot generates stimuli for the vestibular nerves of the lamprey and receives motor commands from the reticular neurons. The final outcome is a sensory–motor behavior of the robot, organized by the connections in the lamprey’s brain’. The team hope to use their neuro-robotic system to find out about the computational properties of synaptic plasticity. Such advances in cybernetics should also speed the development of brain-controlled prostheses.
Stimulating feedback A new study reveals the importance of feedback connections for human visual awareness [Pascual-Leone, A. and Walsh, V. (2001) Science 292, 510–512]. The researchers used transcranial magnetic stimulation (TMS) to excite primary visual cortex, V1, and the visual motion area, V5. This allowed them to work out the relative timing of events in the two areas. Stimulation of visual areas evokes ‘phosphenes’, or unstructured visual sensations. V5 was stimulated above the threshold for phosphenes, and V1 below threshold. V5 stimulation thereby evoked moving phosphenes, whereas V1 stimulation acted as a temporary lesion by introducing local electrical noise. Disrupting V1 activity before V5 stimulation had no effect on the perception of visual motion. However, disrupting V1 activity 5–45 ms after V5 stimulation abolished or reduced the sensation of visual motion. Walsh commented, ‘the work follows earlier TMS studies of blind and blindsighted patients by myself and Cowey, which showed that V5
phosphenes could not be elicited in the absence of V1.’ The study also highlights the strength of TMS as a technique for determining the timing of neural events, as it provides an estimate of the time for signals to travel from one cortical region to another. HJB
James or Jane? Several studies presented at the Vision Sciences Society Conference (Sarasota, USA, May 2001) revealed new findings on how we use vision to judge gender. Michael J. Tarr and his colleagues showed that, because of the reflectance properties of hair and skin, adult faces differ in colour according to gender, with male faces containing relatively more red and female faces more green. An optimal model using colour alone can discriminate the gender of a face with 75% accuracy. Presenting extremely blurred faces, Tarr et al. found that human subjects can also perform rapid sex classification of faces using colour. Also, Ian Thornton and co-workers used ‘point walker’ displays, in which only the motion of several points on the human body is visible, to study how we perceive gender from information about gait. Both men and women, who had to search for male or female walkers from amongst figures of the other sex, were quicker at the search task when the target was of the opposite sex from that of the subject. MW
Animal concepts Animals may possess much more complex concepts that previously thought, and even a form of consciousness, two recent studies report. The honeybee can perform a ‘delayed match-to-sample’ task: when exposed to the color red and later given the choice between red and green, the insect can be trained to choose red. In a recent report, Martin Giurfa and co-workers (Nature 410, 930-933) report that honeybees trained in this way can generalize correctly to previously unseen stimuli, even when in other modalities, and so can be shown to learn and use the abstract concept of ‘same’ (and ‘different’). For instance, when first trained to choose the same color, the insect generalizes and chooses the same shape, or the same smell. In another recent study (Proc. Natl. Acad. Sci. U. S. A. 98, 5359–5362), Robert R.
Hampton suggests that monkeys might possess a form of introspective consciousness previously thought to be unique to humans, namely the knowledge of whether we remember. For instance, says Hampton, we know whether we remember someone’s phone number or not, without having to place a call to test our memory. Monkeys, when given a chance to take a memory test for a reward, or to decline the test but receive a smaller reward, are more likely to decline when their memory is less reliable – showing that the animals have access to their own mental states. MW
It’s not what you look at, it’s what you see New research is showing that the brain reacts not only to a sensory stimulus, but to how, or whether, the stimulus is actually perceived. Studying how monkeys react to hard-to-detect visual stimuli, Hans Supèr and his colleagues (Nat. Neurosci. 4, 304–310) have shown that even neurons in the primary visual cortex are sensitive to the stimulus-perception difference. Although the visual stimulus remains the same, some neurons respond differently depending on whether the stimulus is detected or missed. Another study on monkeys, presented by Ziv Williams and co-workers at the Vision Sciences Society Conference (Sarasota, USA, May 2001), examined the response of neurons in the parietal cortex to ambiguous apparent-motion displays (such as the flashing lights around the edges of signs). After watching the motion, the monkeys indicated the direction in which they perceived it to move. Whereas the stimulus itself was totally ambiguous, Williams et al. found that the discharge of some parietal neurons was correlated with the subjectively perceived direction of motion. MW
Visual illusions and prefrontal cortex A new study demonstrates that prefrontal cortex activity can reflect the perception of a visual illusion [Lebedev, M.A. et al. (2001) J. Neurophysiol. 85, 1395–1411]. The researchers trained a monkey to fixate a spot of light surrounded by a frame of other lights. The lights disappeared and then reappeared, sometimes in a new location. The monkey had to decide whether the spot
http://tics.trends.com 1364-6613/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.