ERIC Number: ED264516
Record Type: Non-Journal
Publication Date: 1985-Jun
Reference Count: N/A
Estimating Frequency and Size of Effects Due to Experimental Manipulations in Eye Movement Research. Technical Report No. 338.
McConkie, George W.; And Others
A study of eye movements was conducted to determine whether the visual regions are perceived in their entirety on each fixation or whether the actual region perceived varies from fixation to fixation. The resulting data were used in a frequency of effects analysis. The frequency of effects problem arises once it has been established that an experimental manipulation has produced an effect, and consists of trying to determine the frequency and size of the effect. Text was displayed on a CRT and refreshed every three milliseconds (msec). The subjects' eyes were monitored during reading, with sampling of eye position every msec. During selected fixations, the letters at certain locations were replaced by other letters, thus resulting in erroneous letters being present at specific retinal locations on those fixations. The eye movement data were then analyzed to determine whether errors produced an effect, and if they did, to estimate the frequency with which this occurred. Subjects were 12 college students, each of whom read 16 short passages, which yielded over 1,000 fixations in the control and two experimental conditions. The results indicated that in one instance, a manipulation that produced a 21-msec increase in fixation duration was actually producing a 151-msec increase in only 21% of the instances and was having no effect in the remaining 79% of the cases. The findings suggest that studies of eye movements in reading should use the frequency of effects analysis procedure to determine more accurately the effects of a given manipulation. (HTH)
Publication Type: Reports - Research
Education Level: N/A
Sponsor: National Inst. of Mental Health (DHHS), Rockville, MD.; National Inst. of Education (ED), Washington, DC.
Authoring Institution: Illinois Univ., Urbana. Center for the Study of Reading.; Bolt, Beranek and Newman, Inc., Cambridge, MA.