The Evolution
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To see why, consider Loftus and Loftus (1974). In this experiment
subjects were able to respond to simultaneously presented category-letter
pairs .13 sec faster than letter-category pairs. Inasmuch as simultaneous
presentation was involved, the difference in reaction times does not
lend itself to explanation through activation asymmetry—it can, however,
be readily attributed to activation interference. Thus one may argue
that the stimulus animal-Z more quickly obtains the response Zebra than
does Z-animal, because memory finds it difficult to keep the part-whole
links of the letter Z activated while going on to read the word animal.
It is interesting that when the same experiment was repeated with a
time interval inserted between the category and the letter, subjects
intersected category-letter pairs .27 sec faster than letter-category
pairs. In other words, the effect that order had on reaction time—what
will be termed the order effect—approximately doubled when a time inter-
val was inserted between the category and the letter. This increase is
readily accounted for by arguing that the addition of the time interval
allows activation asymmetry to have an effect along with activation inter-
ference. Accordingly, both activation interference and activation asymmetry
are useful in explaining Loftus and Loftus (1974).
It should be noted, as Loftus and Loftus point out, that the relatively
small effect (.13 sec) of varying order given simultaneous presentation
may actually be the consequence of simultaneously presented items being
read in the correct order even when they are presented in the wrong order