The Timecourse of Morphological Processing:
Base and surface frequency effects in speed-accuracy tradeoff designs
Jennifer Vannest
University of Michigan
Thanks: Rick Lewis
Keith Johnson
Univ. of Michigan Cognitive Science/Cognitive Neuroscience
University of Michigan fMRI Center
Whole-word vs. decompositional processing
in lexical access of complex words
Dual-route models suggest that both whole-word and decomposed access
representations are used.
However, these models generally do not make claims about the timecourse of
processing.
Base and Surface Frequency Effects
(Taft 1979, Bradley 1979)
Variation in Base Frequency:
agreeable profitable
Variation in Surface Frequency:
acceptable drinkable
Base Frequency effects have been interpreted to indicate morpheme-by-
morpheme processing
Use Base and Surface frequency as predictors in regression analysis
- allows for more stimuli and a wider range of frequencies -- treat frequency
as a continuous variable
Speeded Lexical Decision Task Visual Decision
Presentation Response Auditory Response
of Word Delay Cue (target 400ms)
SUITABLE e.g. 500 ms
Beep! YES or NO
Response Delays: 150, 300, 500, 700 ms
- Response delays are randomized and vary across participants for a given item
- Participants are asked to respond within 400 ms, and given RT feedback
- Response times and error rates at each delay can be predicted from base and surface frequency
Previous Work: Suffixed WordsDerivational suffixes:
-ness (20)
-less (16)
-able (30)
-ity (16)
Inflection:
-ed (30)
Matched as closely as possible for length, base and surface frequency
Previous Work:
Fillers:
- 40 monomorphemic words
-nonwords: 40%
(25 % of those with some morphological structure)
RT and Percentage Errors by
Delay Condition
100
150
200
250
300
350
150 300 500 700
Delay Condition (ms)
RT
0
0.05
0.1
0.15
0.2
150 300 500 700
Delay Condition (ms)
Proportion Errors
150 300 500 700
RT surf -ity
freq -able
effect
-ness -ness
base
freq -able
effect -less -less
-ed -ed -ed
150 300 500 700
ErrorRate
surf -ity
freq
effect
-ness -ness -ness
base
freq -able -able
effect -less -less -less -less
-ness -ness
-ed -ed -ed
General Patterns:
Suffixed words can be sensitive to both base and surface frequency very early in processing (150 ms).
Effects of base and surface frequency may appear in response times, error rates, or both. Effects on error rates are more common at longer delays.
As in standard lexical decision, patterns of frequency effects reveal differences according to linguistic properties. (e.g. surface frequency effects for –ity, base effects for -ed)
However…
The pattern of effects for individual suffixes thus far has been too messy to be informative about the timecourse of processing.
This task is difficult! That fact, in combination with relatively low proportions of “complex” nonwords may have led to task-specific strategies.
Better controls for noise and strategic effects…
Derivational suffixes:
-ness (40)
-less (60)
-able (60)
-ity (60)
Inflection:
-ed (60)
Matched as closely as possible for length, base and surface frequency
Fillers:
-100 monomorphemic words
-nonwords: 47.5%
-63.5% of these had some morphological structure
Varied presentation rate along with response delay
Delay conditions organized into a block design
Block Design:
Response delay for a given item was varied between subjects
Each subject saw 25% of the items at each response delay
Each word type was evenly distributed over the 4 response delays
The order of the response delay sections was pseudo-randomized so that it never consistently increased or decreased
100150200250
300350400
150 300 500 700
response delay (ms)
RT
RT and Percentage Errors by Delay Condition
0
0.05
0.1
0.15
0.2
150 300 500 700
response delay (ms)
Proportion Errors
150 300 500 700
RT surf -ity -ity -ity
freq
effect
-ness
-ed
base -ity
freq -able -able
effect -less -less
-ness -ness
-ed -ed
150 300 500 700
ErrorRate
surf -ity -ity -ity
freq
effect
-ness -ness -ness -ness
-ed -ed
base -ity
freq -able -able
effect -less -less -less -less
-ness -ness -ness
-ed
-block design makes -Block Design replicates many of the patterns of effects from the earlier studies
-Except for –ity response time effects, base frequency effects always occur consecutively with or before surface frequency effects
-Base frequency predicted errors for all words (including –ity!)
-Early sensitivity to morphological structure
-Differences in processing for linguistically different suffix types
Different neural processing systems for “decomposable” suffixed words?
Ullman et al (1997) and Ullman (2001) suggest a role of the basal ganglia and left frontal areas in processing regular suffixes
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