One of the oldest philosophical questions regarding psychology asks how much of our ability to perceive the world is innate and how much is gradually acquired through experience? Some have said that our perceptual abilities are hard wired. That is, they are innate and cannot be modified by subsequent experience. However, on the other extreme, it has been argued that our perceptual abilities are only acquired through experience and are very limited at birth. In this case our nervous system is said to be plastic and mouldable. The purpose of the present lab is to investigate the adaptive abilities of the adult visual system.
Psychologists have used two basic methods to investigate experimental effects on perceptual systems. One involves rearing animals from birth in special visual environments (e.g., total darkness). When a kitten is raised with no visual stimulation other than horizontal black and white stripes, what happens to the kitten's ability to perceive the world? The kitten is able to perceive objects in a horizontal orientation but has marked difficulty dealing with objects in a vertical setting (e.g., going through a picket fence). Results of such studies have indicated that early visual experience contributes importantly to the development of visual abilities.
The second method used to study this question is through the use of special optical devices (e.g. prism goggles) to distort the normal vision of adult participants. How does the adult human react to such a change in visual inputs? After wearing goggles that displace your vision to the right, do you adjust or do you continually make errors?
Experiments indicate that the human nervous system is capable of adapting to some visual distortion. We would, therefore, expect adaptation to occur while wearing distortion prism goggles. In other words while wearing these goggles we adjust for displacement, thus we adapt to the optical distortion. As a result, we don't continuously bump into doorways, or for the purposes of this lab, we miss the target less and less in relation to the amount of practice while wearing the goggles. This process is referred to as visual adaptation.
What will happen after the removal of the distorting goggles? Will we continue to make the necessary adjustments which would once again have us bumping into doors or missing steps? Once the distortion device is removed the individual is likely to still make the required allowances, thus resulting in miscalculations. As a result, the individual will probably bump into a door or for the purposes of this lab miss the target (photograph) in the opposite direction. This disruption or miscalculation is referred to as aftereffects. The aftereffects eventually disappear, but it is not clear as to how long aftereffects should last. Some studies report aftereffects lasting as little as 15 minutes, others as long as two weeks (depending on a number of study parameters).
For the present lab, we will look at how human participants react to distortion of normal vision. For design A there are are two independent variables: practice with three levels, and goggles/no goggles (displacement/aftereffect).
For design B, there are two levels each of practice and of displacement. Lateral error, the dependent variable, is the distance (in cm) by which the target is missed. Importantly, our convention was to deem the target centre as the zero point, the distance to the right as positive and to the left as negative. Thus, if displacement is to the right, you would expect to miss the target in that direction. However, the aftereffect will probably result in missing the target to the left. Would you expect to see participants demonstrate more visual adaptation immediately after putting on the goggles or after they have had them on for 5 minutes? Would the adaptation be more pronounced if they simply had the goggles on or if they practiced throwing the darts at the target, i.e., does time or practice seem to be the most important factor? Would you expect a larger aftereffect with more adaptation? Do you think there will more aftereffect evident if goggles are worn for a short time or for 5 minutes? Would you expect a difference in the aftereffect between groups where participants just wore the goggles for 5 minutes or where they practiced during that 5 minutes?
Most of the class will be used as your participants and will be randomly divided into groups based on the research design used.. Some of you may be required to assist the instructor (allowing for an equal number of participants per group and preventing everyone from harm!). The data for each group will be compiled in the tables below. Do not forget to record the sex and ages of the participants as well.
Materials - 4' X 4' boards with vertical reference lines - photograph/target (12.5cm x 12 cm) - darts - Prism goggles with a 20 dioptre horizontal displacement - rulers - stopwatch
Procedure Students will be randomly assigned to one of three groups: Group A: This group will wear the goggles and throw 1 dart immediately. Group B: This group will wear the goggles and throw 1 dart after 5 minutes. Group C: This group will wear the goggles and throw 30 darts at 10 second intervals.
Each subject shall be individually tested and required to throw darts at the target (a photograph on a vertical black line) placed on a 4' X 8' board at a distance of 5.5 feet. The subject will hold their hands at their side until instructed to throw the next dart.
In Groups A and B, the lateral error (distance in centimetres perpendicular from the centre line) is measured after each dart is thrown. In Group C, the lateral error is measured after the 30th dart is thrown. The data can be recorded in the tables provided below.
Important: Our convention will be to use positive numbers for measurements to the right of the midline and negative values for measurements to the left of the midline.
After the measurement is taken, the subject will then remove his/her goggles and immediately throw another dart. Again, the lateral error will be measured. In this case, it will be a measure of the aftereffect.
There will be three targets set up and one or two people (volunteers from the class) will assist at each target: one person to time the seconds between throws (Group C) or stagger the times that the participants put on goggles (Group B) and one person to measure the lateral error.
2X2 between subjects design; 2 IV's ; practice, visual displacement 1 DV lateral distance from target (error)
4 Conditions: [no goggles; no practice][ no goggles; practice][ goggles; no practice][ goggles; practice]
Note: all participants are run individually. If you are in the goggles on groups , do not put them on before it is your turn.
Condition 1: this group does not wear the goggles and does not practice. They throw 1 dart at the board and measure the lateral distance (error) to the left (-) or to the right (+) of the target
Condition 2: this group does not wear the goggles and throws 1 dart every 15 seconds for two minutes (8 darts). Then they throw 1 more dart for which the lateral distance in cm is measured. (-)to the left and (+) to the right of the target
Condition 3: this group wear the goggles for a period of two minutes facing away from the target, and after the two minutes, throws a dart with the goggles on, and measures the lateral distance in cm from the target (-) to the left and (+) to the right
Condition 4: this group puts on the
goggles (with eyes closed). When they open their eyes, throws a dart every
15secs for 2 minutes (8 darts), then throws 1 more dart and measures the
lateral distance from the target in cm for the last dart thrown. (-)to
the left of the target and (+) to the right.
Design A: A 2x3 ANOVA (mixed design) will be used to analyse the data. From the ANOVA, you will be able to see if there are main effects for Group, main effects for goggles/no goggles and an interaction between the two.
If there are significant main effects, you will do four planned ttests. For displacement (wearing goggles) compare: (1) Group A to Group B and (2) Group B to Group C. For aftereffect (no goggles) compare: (3) Group A to Group B and (4) Group B to Group C.
Your results section you should also
describe the means and sd's for each of the six combinations as well as
a bargraph of these means. Use significance level of =.05.
Design B: A 2x2 ANOVA will be used to analyse the data. Determine whether there are main effects for practice and displacement and an interaction between the two.
Your results section you should also describe the means and sd's for each of the four combinations as well as a graph of these means. Use significance level of =.05.
In your discussion, you need to first note if your hypotheses were supported and then discuss the results. The main results are discussed first and then the more specific ones. Talk about your results in terms of the variables under study (practice, displacement, adaptation) How do your findings relate to the studies outlined in your introduction? How do the findings relate to real life? What can we assume from the results? Recommendations for future research?
Ebenholtz, S. & Fisher, S.K. (1982). Distance adaptation depends upon plasticity in the oculomotor control system. Perception & Psychophysics, 31, 551-560.
Lackner, J. & Lobovits, D. (1977). Adaptation to displaced vision: Evidence for prolonged aftereffects. Quarterly Journal of Experimental Psychology, 29, 65-69.
Redding, G. & Wallace, B. (1988a). Adaptive mechanisms in perceptual - motor coordination: Components of prism adaptation. Journal of Motor Behaviour, 20, 242-254.
Redding, G. & Wallace, B. (1988b). Components of prism adaptation in terminal and concurrent exposure: Organization of the eye-hand coordination loop. Perception & Psychophysics, 44, 59-68.
Redding, G. & Wallace, B. (1990). Effects on prism adaptation of duration and timing of visual feedback during pointing. Journal of Motor Behaviour, 22, 209-224.
Wallace, B. & Fisher, L. (1984). The roles of target and eye motion in the production of the visual shift in prism adaptation. Journal of General Psychology, 110, 251-262.
Some search terms to get you started:
Visual Adaptation, Visual Aftereffects, Displaced Vision.
The data file has been sent to you via
e-mail as an attachment. To retrieve it, go into Pegasus mail for windows.
Click on the new mail button (2nd button from the left). Highlight the
message and click on open. It will say, "This message has attachments",
click on the attachment button at the top of the message. Click on the
save button in the attachment box. Now you have to specify where you want
to save to: your f directory is probably the most useful, unless you want
to put it on disk. Click on the drives arrow and select the appropriate
drive. Click on OK, then click on Done in message attachments. Now, when
you go into SPSSwin you can open the data file by specifying the appropriate
directory and drive.
For the 2X2 between design, use the General Linear Models: Simple Factorial command.
Put the appropriate variable selections in the dependent and Factors boxes. For each factor (ie. goggles, practice) identify the minimum and maximum values found in the respective column in the data file by clicking on the Define Range button. Click continue.
To get cell means, under the Analyze menu, select Compare Means, and then Means.
Identify the dependent variable (s), move one of the independent variables (or factors) into the IV box, click the Nextbutton, (it will disappear) then move the next iv to the iv box. Click on OK.
Alternatively, while in the Simple Factorial dialog box, one can click on Options, click on the circle beside hierarchicalor experimental type of method, and then put an beside Means and Counts in the statistics box.
You will also want Descriptives of your sample, and a graph to illustrate results