In order to assess whether the basic sensory finding had been replicated, it was necessary
to ascertain whether the large-capacity finding was obtained separately for the
selection-by-row and the selection-by-category conditions. For this purpose, the subjects'
whole-report performance was treated as the control ISI level. Their partial-report data in
the practice session were excluded. The subjects' performance on both tasks was then
subjected to a 2 (recall instruction) x 2 (perceptual grouping) x 5 (ISI and whole report)
factorial ANOVA with repeated measures on all factors.
The mean square error term for the ISI x recall instruction interaction was used to derive
the standard error of the difference for the two series of planned t-statistic comparison
tabulated in Table 5 (Wiper, 1962). As can be seen from Table 5, partial report is superior
to whole report at delays shorter than 1 sec when selection is by row. When selection is
by category, partial report is no better than whole report even when ISI is 0 msec.
Table 5
Planned Comparisons Between Partial Report and Whole Report
at Various ISI Levels (in Milliseconds) for the Spatial
Selection (Left Panel) and the Category Selection
(Right Panel) Conditions in Experiment 2
|
______Selection by Row______ |
_____Selection by Column | |||||||||
|
0 |
150 |
500 |
1000 |
0 |
150 |
500 |
1000 |
WRa | ||
|
PRb |
6.29 |
5.93 |
5.07 |
3.35 |
4.55 |
4.49 |
4.32 |
3.90 |
3.46 | |
|
>WRc |
2.83 |
2.47 |
1.61 |
-0.11 |
1.09 |
1.04 |
0.44 |
0.44 | ||
|
t |
5.55* |
4.84* |
Ξ S 3.16 |
-0.22 |
2.14 |
2.04 |
0.86 |
0.86 | ||
aWR = whole report (mean number of items recalled). b PR = partial report (mean
number of items available). c > WR = magnitude of the partial-report superiority (partial
report minus whole report). *Significant at the .05 level for the entire set of comparisons.
Critical t(with k = 5; df for MSe = 20; n = 6) = 2.30.
Discussion
A comment on the top panel of Figure 5 is helpful here. It is obvious that it may not be
easy to perceive the triangle gestalt formed by the three letters. However, to appreciate
Experiment 2, it is necessary to distinguish between what a theoretical position prescribes
one should be able to do and what one actually can do.
The perceptual grouping hypothesis, together with the assumption that category
information is available as a result of a brief stimulus exposure, prescribes that our
perceptual system is capable of picking up the triangle in the top panel of Figure 5 so
readily that a partial-report superiority by category should be observed. Whether the