MadSci Network: Neuroscience |
Dear Asim, You can estimate reaction times by asking, for example, a subject to press a level when he/she sees a light and to do it as fast as possible. In this situation, the light stimulates receptors in the retina, producing impulses in the optic nerve and transmitting information to visual areas of the brain. From these areas, information is likely to be transferred to motor areas of the brain which then send efferents to the motoneurones of the spinal chord, which in turn send impulses to the muscles. All this takes some time, which is called « reaction time ». When testing reaction time in a reflex behaviour (ex. knee jerk), one will find that it is much faster : this is because the sensory nerves that are stimulated when tapping the tendon send the information directly to the motoneurons of the spinal chord. Similarly, when a nociceptive stimulus (ex. electric shock) is applied, the limb is moved without the control of the brain. However, the nociceptive reflex is somewhat slower that the knee jerk, in part because the nociceptive fibres are slower but nevertheless, the reaction time is faster than auditory or visual. The auditory reaction time is also usually faster than the visual, although this may be relative to the stimuli used to assess the reaction time. That is possibly due in part to the differences between auditory and visual receptors ; the visual involve more chemical reactions whereas the auditory is mechanical. Moreover, sensory reaction time also depends on the attentional state and on training. If you introduce a « pre-signal » that warns the subject that the actual signal will arrive in, say, a second, this will diminish the reaction time. Finally, it worth mentioning that there are great inter- individual differences. I hope this helps ! Eric
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