Word Recognition Experiment

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Introduction
Task and Stimuli
Design
Procedure
Analysis
Data Format
References


Introduction
Studies of the intact human brain have contributed to the literature on hemispheric specialization. A technique that has made this possible is the divided visual field technique pioneered by Barton, Goodglass, & Shai (1965) in which vertically oriented words are flashed to the left or right of a fixation point for periods of time that permit recognition but that are too fast to allow eye movement. Using this methodology it is possible to fix the retinal locus at which the word appears in the right and left eyes and thereby route the retinal information selectively to either the right or the left hemisphere. The diagram below explains why. Verbally the explanation is that visual information from the right retinal hemifield of both eyes (which is from the left visual field) is routed to the right hemisphere of the brain whereas visual information from the left retinal hemifield (which comes from the right visual field) is routed to the left hemisphere of the brain. This arrangement results in "processing priority" for one hemisphere over the other. The priority would not be present for information presented at the midline where it would find its way to both hemispheres simultaneously.
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Task and Stimuli

wpe1.jpg (12044 bytes)The task involves identifying each of 16 words as they are presented serially on the screen. Following each presentation, participants are asked to identify the word by typing it in a text entry box. The stimuli for the task are 16 5-letter English words, all of which are common but relatively low in frequency. Half of the words are presented in the right visual field and half in the left. Order of words as well their left-right assignment is random.
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Design

The single within subject variable for the study is the visual field in which a word is presented. The dependent variable is the display time for the word on the trial it was recognized. Display times begin at 90 sec for the first presentation of a word and increment by 10 msec until the word is recognized.
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Procedure
Whereas there are 16 words to be recognized the actual number of trials is indeterminate because the experiment continues until all words have been recognized correctly. Each trial begins with a pulsating plus sign that appears in the middle of the screen. This is to assure central fixation. To initiate a trial, the participant presses a key. The pulsating plus sign stays on the screen for a period of 3 to 5 seconds before a word is presented. The random delay is designed to prevent anticipation of the word's appearance. The display time is variable, as described above and depends on how many times the word has been presented before. Once a word is recognized it is removed from the presentation list.
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Analysis
The simplest analysis is to compare mean recognition times for the set of 8 words that appeared on the right and the 8 that appeared on the left. To test the significance of the left-right difference in means, a related samples t-test can be used. In large data sets, however, it is interesting to add gender as a between subjects variable in the analysis. There is considerable evidence that females on average are less lateralized than males (see Hiscock, Israelian, Inch, Jacek, & Hiscock-Kalil, 1995 for a review), which would be reflected in smaller left-right mean differences for females than males. The significance of the difference could be determined using the interaction term of a two-way analysis of variance that treats visual field as a within subjects factor and gender as a between subjects factor.
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Data Format in Downloadable csv file
The data obtained via the Download data link on the PsychExperiments homepage are comma delimited.  The first entry (up to the first comma) is the affiliation of the research participant.  Typically this is the class to which the participant belongs.  Non-affiliated participants use the default entry of Interested Person. Next is the randomly assigned ID code for the research participant. The third and fourth entries are the data and time (24-hour format) on the server when the data were received.  Next come an entry for the gender of the participant ("M" or :F"), handedness of the participant ("R" for right, "L" for left, and "M" for mixed), and age of the participant.  Next are the raw data for the experiment organized by trial number. Trial numbers are from 1 to 16 because there were 16 words to be recognized.  After the trial number are text entries to indicate the word and its location relative to the fixation point.  Next is the display time (seconds) on the trial when the word was recognized correctly. The table below shows the format for the trial data in tabular form.  Not included in the tabular display are the user information (affiliation, ID, data, time, gender, etc.) which precede these data, as shown in the text line below the table. 

Trial Number Word Location Display Time Trial Number Word Location Display Time Trial Number etc.
1, HINGE, left, .10, 2, DEBIT, Left, .11, 3, etc.

U. of Mississippi--Carvers Psy 214,CWS740,7/28/2002,15:23,M,R,20,1,HINGE,Left,0.10,2,DEBIT,Left,0.11,. . .,16,BLEND,Right,0.09,

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References

Barton, M.I. , Goodglass, J.L., & Shaii, A. (1965). Differential recognition of tachistoscopically presented English and Hebrew words in right and left visual fields. Perceptual and Motor Sills, 21, 431-437.

Bryden, M.P. & Ramey, C. (1963). Left-right differences in tachistoscopic recognition. Journal of Experimental Psychology, 23, 445-458.

Hiscock, M., Israelian, M.,Inch, R., Jacek, C., & Hiscock-Kalil, C. (1995). Is there a sex difference in human laterality? II. An exhaustive survey of visual laterality studies from six neuropsychology journals. Journal of clinical and experimental neuropsychology, 17, 590-610.

Springer, S.P. & Deutsch, G. (1989). Left brain, right brain. New York: W.H. Freeman.
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Last revised:November 01, 2003 07:01:31 PM
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