Ambiguity and frequency effects in regular verb inflection
Mary L. Hare
Bowling Green State University
Michael Ford and William D. Marslen-Wilson
Brain and Cognition Unit, Cambridge University
Frequency and Ambiguity effects in English verb inflection
An important issue in lexical representation, and in cognitive science more generally, is
whether regularly inflected nouns and verbs are represented and accessed in a qualitatively
different way than are irregulars. At least one influential account assumes that irregularly
inflected items are represented lexically, independent of their stems, but those with regular
inflection are not - instead only the stem is found in the lexicon, and inflected forms are
produced through application of a rule once the stem has been. In contrast, a number of other
accounts take what has been termed a fuill-listing approach, in which both regularly and
irregularly inflected forms can be represented as single units.
The two accounts make very different predictions about the role of frequency in the
processing of regular past tense verbs. The first, or dual-mechanism, model claims that irregular
past tenses are lexical items, so the frequency of use of an irregular past tense should affect its
speed of access. For regular past tenses, however, access should be influenced not by past tense
frequency, but by the frequency of the verb stem, which must be accessed before the past tense
rule applies. By contrast, a full-listing account assumes that both regular and irregular past tense
verbs have a lexical representation, so frequency of use should also have an effect on the access
of regular pasts.
To test between these two predictions we look at competition effects in ambiguous past
tense verbs. We use two experimental tasks, writing to dictation and primed lexical decision. In
both tasks the test items include regular and irregular past tense verbs with unrelated
homophones, such as allowed/aloud or blew/blue. The items chosen differed in their relative
past tense/homophone frequencies, so that in one condition the past tense was the more frequent
reading, while in a second the homophone was more frequent. The question of interest was
whether this frequency manipulation affected responses to both regular and irregular verbs, or
whether effects were found for the irregulars alone.
In Experiment One subjects heard a list of words and wrote a phrase or sentence
containing each word. The results show strong effects of past tense frequency, with significantly
more past tense responses when the past tense interpretation was more frequent than the
competing homophone. The simplest explanation of these results is that subjects wrote the first
item accessed when the ambiguous input was heard, and that the most frequent of the two
meanings was accessed first. Crucially, this was the case for both the regular and the irregular
verbs.
Experiment Two tested whether the same ambiguous past tense verbs prime their stems
in a lexical decision task. Here subjects heard the ambiguous form, and immediately at the offset
of the spoken prime the related verb stem appeared on a computer screen in front of them.
Subjects made a lexical decision to the visually presented stem. Again, we find a significant
effect of past tense frequency in the Regular verbs: Reaction times are faster after test than
control when the past tense prime is more frequent than its homophone, but slower after test than
control when the homophone interpretation is more frequent. Importantly, regression analyses
rule out the alternative explanation that stem frequency is the crucial factor.
This pattern of results is clearly inconsistent with any account in which effects of past
tense frequency must vary with the regularity of the verb. We discuss the implications for
claims about the lexical representation of morphologically complex forms.