Because the three experiments to be reported followed the same general
procedure, the method used is first presented in general terms. Specific departures from
this general procedure will be described when applicable.
Subjects
A separate group of 14 subjects was run in each of the three experiments. Subjects
in Experiments 1 and 2 were first-year psychology students who participated for two
bonus marks. The group of subjects in Experiments 3 consisted of some undergraduate
students and some members of the staff of the Department of Psychology at the
University of Wollongong. All subjects were naive as to the theoretical expectations of
the experiments. All subjects reported normal or corrected-to-normal vision.
Apparatus
Stimulus items were selected and presented with a PDP/I 1-23 microcomputer
driving a CIT-100 CRT The type of phosphor used in the CRT is P-31 (green), which
decays to the minimum discernible brightness in a brightly lit room in 38 μs, a condition
used in this study. The stimulus duration and the ISI manipulation were timed with a
programmable KW V I 1 A clock under the control of the program.
Materials
A seven-item array was presented to the subject on every trial. Seven consonants
were selected randomly, without replacement, from an ensemble of 20 consonants. That
is, the five vowels and the letter Y were not used in the experiment. A question mark was
used as the partial-report probe. When applicable, a masking array (made up of seven
grids of dots) was used as the mask.
Each letter was made up of 7 X 9 (points) grid subtending a visual angle of 20'
horizontally and 38' vertically. The seven-item array subtended a visual angle of 2° 36'
horizontally and 38' vertically
Design
A 2 X 5 complete factorial analysis of variance (ANOVA) with repeated measures on
both factors was used in all three experiments. The first factor was the absence or
presence of backward masking. The second factor was the ISI between the offset of the
stimulus array and the onset of the partial-report probe and/or the mask. Because the
three experiments differed in what was being delayed as well as the exact values for the
five delay intervals, this factor will be described individually for each experiment.
Procedure