Word Length and PI 1
Complete Citation: Tehan, Gerald and Turcotte, Josée (2002). Word length effects
are not due to proactive interference. Memory, 10 (2), 139-150. ISSN 0965-8211.
Accessed from USQ ePrints
http://eprints.usq.edu.au
Word Length Effects Are Not Due to Proactive Interference
Gerald Tehan
University of Southern Queensland
Toowoomba, Queensland, Australia
Josée Turcotte
Laval University
Québec, Québec, Canada
Mailing Address:
Gerry Tehan
Department of Psychology
University of Southern Queensland
Toowoomba, 4350
AUSTRALIA
Phone number: (07) 4631 2376
e-mail: tehan@usq.edu.au
Word Length and PI 2
Abstract
In immediate serial recall short words are better recalled than long words. The
word length effect has become pivotal in the development of short-term memory
models. The current research tests one explanation of the word length effect; that it is
related to proactive interference (PI). We report two experiments in which the
relationship is directly tested. In the first experiment we show that word length effects
can be observed over the first few trials in an experiment and that the effect shows
itself primarily in the number of omissions made. In the second experiment we
simultaneously test for PI and word length effects. Strong word length effects were
present but there was little evidence for PI influencing either overall levels of recall or
the word length effect. In short, no empirical support was found for PI as an
explanation of the word length effect.
Word Length and PI 3
Word Length Effects Are Not Due to Proactive Interference
Across the years there has been continual debate concerning whether
forgetting is caused by decay or by interference. One interesting facet of this debate is
that interference effects are usually seen as a prime source of forgetting in long-term
memory settings, but decay is seen as the principle means in immediate memory
settings (Baddeley, 1986; Burgess & Hitch, 1996; Henson, 1998; Page & Norris,
1998). Consequently, over the last thirty years or so, the vast majority of models of
immediate memory have assumed that the short-term memory trace that supports
immediate recall decays very rapidly, unless it is renewed by verbal rehearsal. Not
surprisingly these models are now often referred to by the generic name of "trace
decay plus rehearsal" models (Brown & Hulme, 1995).
For those who argue in support of decay, the word length effect, the fact that
span for short words is larger than span for long words, is one of the key short-term
phenomena. In the original research that established this effect, Baddeley, Thomson
and Buchanan (1975) first established a span advantage for one-syllable words over
five syllable words. However, in subsequent experiments they established that the
prime determinant of the word length effect was the spoken duration of the words.
Span for the short duration words was significantly larger than span for the long
duration words. On the basis of such findings the decay plus rehearsal models assume
that short-term memory traces rapidly decay in real time. Given that per given period
of time more short words can be rehearsed than long words, more short words can be
kept in an active state than long words.
In recent years, however, the trace decay plus rehearsal assumptions have
come under increasing amounts of pressure. The initial research that implicated
spoken duration has proved difficult to replicate (Lovatt, Avons & Masterson, 2000).
Word Length and PI 4
Word length effects have been found when pronunciation rates have been controlled
for (Caplan, Rochon & Waters, 1992), or rehearsal has been prevented (LaPointe &
Engle, 1990) and there are instances of where there are no-span differences where
there are clear differences in pronunciation rates (Service, 1998). Cowan et al (1992,
see also Dosher & Ma, 1998) have suggested that word length effects occur during the
recall process itself rather than during rehearsal prior to recall. In short, simple decay
notions appear to be inadequate as either a necessary or sufficient explanation for the
word length effect.
Currently, there are three alternative explanations for the word length effect,
two of which are based upon interference assumptions. Neath and Nairne (1995)
suggested that word length effects might result from intra unit interference. Melton
(1963) had demonstrated that items within a study list produced mutual interference
on each other. Neath and Nairne extended Melton's idea to features within words.
They suggested that words had to be compiled from sets of smaller features and that
the more features that had to be compiled, the greater the likelihood that an error
would be made. Since long words were assumed to require the compilation of more
features than short words, these words would be more error prone. Neath and Nairne
incorporated these ideas into the feature model (Nairne 1990) and were able to
provide good fits of existing data. The feature model with its assumptions about intra
unit interference has subsequently made novel predictions concerning the conditions
under which the word length effect would and would not be found and the data have
so far been consistent with the predictions of the model (Neath, Surprenant &
LeCompte, 1998)
The second interference-based explanation is that proactive interference (PI)
plays a role in producing the word length effect (Nairne, Neath & Serra, 1997).
Word Length and PI 5
Nairne et al. argued that if decay was the causal factor underpinning the word length
effect the effect should be as strong on the first trial of an experiment as on the last.
Consequently, they examined performance on a trial-by-trial basis. In their first
experiment they presented subjects with four 5-word lists that consisted of two-
syllable words that differed in spoken duration (Cowan et al., 1992). 220 students
were given four trials of short words and another group of 220 students was given
four trials of long words. No word length effects were present on any of the trials.
This result could be simply interpreted as another failure to replicate previous
findings, or simply be a cohort difference. However, these explanations were ruled
out in the second experiment where subjects studied 24 trials of either short or long
words. Again word length effects were absent on the first four trials, but they did
emerge on the next block of four trials and were also present on the remaining blocks
in the experiment. This finding that word length only emerged after four trials was
clearly problematic for trace decay plus rehearsal explanations. Moreover, the result
was reminiscent of Keppel and Underwood's (1962) finding that forgetting in the
Brown-Peterson task gradually emerged over three or four trials. Given this
correspondence and the fact that the Keppel and Underwood data are generally
attributed to PI, they suggested that word length effects could be related to PI. Thus,
both PI and word length effects build up over trials.
From a theoretical perspective, while the similarities between the Nairne et al
and the Keppel and Underwood are enticing, it is hard to see how word length effects
could be incorporated within standard trace discrimination explanations of PI. The
standard explanation of PI in the Brown-Peterson task is that on the first trial there are
only a small number of items available for recall. There are no problems in
discriminating these items from other items in the experiment because as yet there are