Becker Jordan K361-301 Lab #3 Visual Perception Prism Experiment Introduction: Our senses provide us with the information about the surrounding environment. Vision, especially, provides the mind with information regarding the objects moving around the body. Many times, and under many circumstances, the mind perceives visual stimuli that may not actually represent the actual characteristics of those stimuli. One example is the phenomena of visual illusions (Muller-Iyer or Ebbinhaus-Titchener illusions) which trick the mind by using surrounding stimuli to affect the perceived size of another shape (Class notes, 2008). The effect of those illusions, along with neurological pathologies like optic ataxia and visual agnosia, are due to the fact that the brain has two visual systems. The Focal System is used to identify and recognize static objects; a visual system for perception. The Ambient System is used to identify and detect moving objects; a visual system for action. (Class notes, 2008). With such a complicated visual processing system how does the human mind identify stimuli, select responses, program that response, and then adjust for moving objects and changes in the environment? It has been suggested that a closed loop control system is used to continually process information by using feedback in the form of an efference copy (Magill, 2007). By sending information from the efference copy back through the information process model, the mind adjusts responses. Two theories have been proposed to explain object contact. The cognitive theory states information is not perceived as meaningful until cognitive processes have been performed (Class notes, 2008). The ecological theory states that meaning about visual information can be directly extracted from the environment without the need for cognitive processes (Class notes, 2008). In this experiment, visual information is changed and the mind is asked/forced to respond to the change to maintain successful aiming and throwing of the Zelcro ball. What will happen after the goggles are removed? It might be hypothesized that during `goggled' trials the brain rewires vision perception and upon removal the perception is still cued for the previously goggled vision. Analysis: In this experiment trials were performed where a ball was thrown at a target measuring horizontal variation; there were ten trials with normal vision followed by 30 goggled vision, ending with ten normal vision trials. Error was only measured on a horizontal scale. Subject remained seated the entire experiment and attempted refrain to from moving their head in between trials.
Table 2 Trial Group 1-10 11-20 21-30 31-40 41-50 See graph.
Absolute Error 7.5 9.4 9.6 6.6 6.5
Constant Error 3.0 8.4 9.0 4.6 -4.5
Variable Error 10.19 6.26 7.96 7.90 9.42
Discussion: When the goggles are first put on throw scores tended to increase in error with a positive bias. As more trials are completed, practicing with goggles on helps throw scores and error decreases and accuracy improves. When the goggles are removed, throw scores immediately polarize to the left or negative side and then move back to the target and accuracy improves greatly. If one hypothesized that adapting to the prism goggles occurs by a conscious strategy, when the goggles were removed the subject would not see any compensatory left shifting in throw scores. The subject would continue to throw with the same accuracy as when wearing the glasses as well as in the original trials (ignoring practice effects). However, one could think the prism adaptation occurred by a recalibration of visual processing by which one takes visual information to encode motor commands. If this were true, a subject would have increases in error upon wearing the glasses. With increasing trials, the brain rewires itself to compensate for error and increase accuracy. When the glasses are then removed, the brain remains wired for compensation. One would observe throws to be polarized to the other side because the brain sees the target and encodes a throw that remains compensatory. This compensatory throw, however, is too far left because when the goggles were on the subject threw the ball `to the left' because the prism obscures the target to the right of the field. We do see that throws were very left/negative when the glasses were removed. This supports a brain recalibration and a compensatory mechanism. The following graph shows plots for a patient with cerebellar dysfunction. These patients are unable to recalibrate their gaze-throw directions due to prism vision.
Conclusion: As is demonstrated in the data, gaze-throw adaptations occur by a brain recalibration of the visual processing during prism obscured perception. Thus, the working hypothesis is supported in the data and in the proposed graph of cerebellar dysfunctive patients data. One might however employ a conscious strategy during prism trials to improve scores by ignoring what the eyes are telling the brain. This is extremely difficult because human vision is the premier overriding sense and is almost impossible to overcome by ignorance of perception.