Interocular Transfer of the Motion Aftereffect, Psychology, College Term Papers.com


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Interocular Transfer of the Motion Aftereffect

Interocular Transfer of the Motion Aftereffect A prominent phenomenon in the field of visual science is the motion after-effect (MAE) which is believed to provide a way of bringing together current knowledge of neurophysiology with a measurable visual phenomenon. The MAE is described as a visual illusion produced by viewing any number of motion types (i.e. lateral or vertical linear, spiral, radial or rotation). By viewing a moving physical object for a period of time until the eyes is adapted to the motion. When the motion of the object is stopped, but viewing remains focussed on the object, the viewer may report a slower, reversed/negative movement of the now stationary object (Mather et al, 1998). The history of recognition and research into the MAE phenomenon can be traced back as far as the Aristotelian era. Both Aristotle (330 B.C) and Lucretius (approx. Three centuries later) reported the visual phenomenon as an effect of the stimulus water (although Lucretius went further by describing a MAE direction). It was not until the early nineteenth century that further research was noted. Purkinje (1820) and Addams (1834) both reported the causation and directional flow of the MAE with reference to cavalry parades and waterfalls as their respective motion examples. From this period up until the mid-twentieth century further research had been sporadic. This is perhaps due to the fact that so little was known of the neuroanatomy of the visual system. Wohlgemuth (1911) had however reviewed many of his predecessors work as well as reporting many of his own studies. An important aspect of his research came with the discovery of the storage effect of MAE’s. After adaptation to stimuli, the testing eye is closed for the period deemed to be the length of time for that particular MAE. It is then opened to focus on the now stationary object. Wohlgemuth (1911) found there was still a slight trace of MAE (as if the closing of the eye had put the MAE on hold). Since the mid-twentieth century however, there has been escalation in the amount of interest paid to MAE’s. This may well be due to extensive advancements made in neuroscience which subsequently opened many doors to other areas of research; one being that of the visual cortex (Mather et al, 1998). Contemporary theory regarding MAE stipulate either of three types of test stimulus, The neutral test method is either a motionless or energetic with no preference to direction. The null test method is an energetic test with a preference for directional bias in order to null the MAE. The transfer method, although regarded as similar to the first two methods, is different due to the way it compares measurements of MAE’s between different adaptation and test stimuli. The current study design looks at the difference in MAE magnitudes between monocular (MON) and interocular transfer (IOT) viewing conditions. It is suggested (Wade, 1991) that IOT MAE’s are of a lesser magnitude than monocular MAE’s. At the same time it is impressive that IOT allows an MAE. Blake et al (1981) give evidence to suggest that neurons in the visual cortex are all connected and benefit from stimuli whether adapted to it or not. Although complete IOT is said to be hypothetical, their evidence suggests that “two eyes constitute a single visual channel” (Blake et al, 1981). This is in line with the cyclopean theory (Wade et al, 1991). This study used a 2x2 within subjects factorial design. The factor Viewing Condition has two levels (Monocular and interocular transfer) of testing with which the factor Eye adapted (having two levels, dominant and non-dominant eye) is tested. The dependent variable is the comparison of performance between the dominant and non-dominant eye testing and how long the after-effect lasts. The hypothesis was that there will be a monocular viewing will produce a higher magnitude (seconds) than interocular transfer, and that dominant eye adaptation will also yield a higher magnitude than non-dominant eye adaptation. There were a total of 34 subjects. All subjects (male and female) were students of the University of Dundee participating in a projects meeting. On arrival at the projects meeting, all subjects were briefed on the theories of motion adaptation and motion after-effect (MAE) and their relevance to the physiology of the visual cortex. The experiment required subjects to be tested for sight dominance using the ‘hole in the card’ test. From this, sight dominance is reported in either left or right eye. Subjects are subsequently tested for MAE’s using random sequences of the four testing conditions. These 4 testing conditions are the two viewing conditions (Monocular and interocular transfer) utilising each of the eye adaptations (dominant and non-dominant) in both conditions. In order to measure the length of the MAE in each condition; the subject is seated about 1 metre from a spiral-patterned disc, which they are to observe while the disc rotates and while it is stopped until the MAE ceases. The disc rotates at an angular velocity of about 60 degrees per second for 30 seconds (per eye adaptation). The disc stops immediately on 30 seconds. A timing device (i.e. stopwatch) measures the length of each of the 4 randomly sequenced MAE conditions. Under each condition, subjects are to perform viewing of a spiral patterned disc in motion and then the same patterned disc is to be viewed stationary with one eye only. Eye occlusion is achieved by covering the non-adaptation-tested eye with one hand. All subjects then participate in the experiment adhering to the guidelines and the experiment concludes once the experimenter collates all magnitude scores. Mean MAE magnitudes (seconds) and their S.D.’s for each Viewing condition are shown in Table 1. Table 1. Means of performance by viewing condition by eye adapted (S.D.’s in brackets). Viewing condition Dominant Non Dominant A 2x2 within subjects analysis of variance (ANOVA) was carried out on mean MAE magnitudes (seconds) by viewing condition with eye adapted and the analysis are summarised in Table 2. Table 2. Summary table for ANOVA of MAE magnitudes for two levels of Viewing condition and two levels of Eye adapted. Source VIEWCOND EYEADAPT SS df MS F P. VIEWCOND Linear 283.047 1 283.047 35.683 *0.001 Error(VIEWCOND) Linear 261.763 33 7.932 EYEADAPT Linear 2.436 1 2.436 .410 NS Error(EYEADAPT) Linear 195.854 33 5.935 VIEWCOND * EYEADAPT Linear Linear .922 1 .922 .212 NS Error(VIEWCOND*EYEADAPT) Linear Linear 143.308 33 4.343 The main effect of viewing condition was statistically significant (F(1,33)=35.683; p*0.001]. The main effect of eye adapted was not found to be statistically significant. Also there was no significant interaction between viewing condition and eye adapted. Mean MAE magnitudes (seconds) for levels of viewing condition and eye adapted are shown in Figure 1. Figure 1. Profile Plot depicting mean magnitude (seconds) for levels of viewing condition and eye adapted. There was no significant interaction between viewing condition and eye adapted, although it can be seen that there is a consistency with reduction in MAE magnitude from monocular testing to interocular testing. Through analysis of the results, it may initially seem that the experimental hypothesis is supported. The encoding category shows that there is no significant main effect between recall scores for visual and auditory encoding preference subjects. The learning instruction method factor however, shows that performance between the two groups has a highly significant main effect at the 1% level. It can also be seen from Table 2. and the profile plot in Figure 1. that there is a significant interaction (at the 5%) between the visual and auditory encoding groups across the imagery and sentence conditions. This in turn suggests that the experimental hypothesis cannot be wholly accepted. Bibliography:

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