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Chapter 8

Chapter 8 (Part 2)

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PSYC 2390
Lana Trick

Chapter 8 Perceiving MotionTaking Eye Motions Into Account The Corollary Dischargecorollary discharge theory the perceptual system uses a signal called the corollary discharge to take into account the fact that the observers eye is moving Corollary Discharge TheoryEyes move because motor signals are being sent from the motor area of the brain to your eye musclesCorollary discharge signal splits off from the motor signalCDS occurs anytime a motor signal is sent to the eye muscles indicates that a signal has been sent from the brain to move the eye CDS reaches a hypothetical structure called the comparator which relays information back to the brain that they eye is moving Corollary Discharge Theory If there is no movement of an image across the retina but the comparator is receiving information indicating that the eye is moving then the observer perceives motioncomparator not only receives the CDS but also receives the signal that occurs when an image moves across the retina This movement activates the retinal receptors and sends a signal out the optic nerve that we will call the image displacement signal IDSWhen the IDS reaches the comparator it sends a signal to the brain that results in the perception of motion This occurs with either a signal that the eye is moving CDS or a signal that an image is being displaced across the retina IDSCDS is generated because the eye is movingm and an IDS is generated because images of the scene are sweeping across the retina When both the CDS and IDS reach the comparator simultaneously no signal is sent to the brain so no motion is perceived both behavioural and physiological evidence that supports the theoryBehavioural Demonstrations of Corollary Discharge TheoryCreate situations in which motion perception occurs even though there is no motion across the retinaAfterimages appears to move when you move your eyesWithout motion of the stimulus across the retina there is no image displacement signal However a corollary discharge signal accompanies the motor signals sent to your eye muscles as you move your eyes Only the corollary discharge signal reaches the comparator and you see the afterimage moveSee motion when you push on your eyeballStark and Bridgeman lack of movement occurred because the observers eye muscles were pushing back against the force of the finger to keep the eye in place Corollary Discharge Theory the motor signal sent to the eye muscles to hold the eye in place created a corollary discharge signal which reached the comparator alone Stark and Bridgemans observers saw the scene move Corollary discharge theory proposed that there is a signal that indicates when the observer moves or tries to move his or her eyes Physiological Evidence for Corollary Discharge TheoryCorollary Discharge signal but no image displacement signal in both demonstrations
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