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The Timecourse of Morphological Processing: Base and surface frequency effects in speed-accuracy tradeoff designs

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

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The Timecourse of Morphological Processing: Base and surface frequency effects in speed-accuracy tradeoff designs

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  1. 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

  2. Whole-word vs. decompositional processing in lexical accessof 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.

  3. Base and Surface Frequency Effects (Taft 1979, Bradley 1979) Variation in Base Frequency: agreeable profitable Variation in Surface Frequency: acceptabledrinkable

  4. Base Frequency effects have been interpreted to indicate morpheme-by-morpheme processingUse 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

  5. Visual Decision Presentation Response Auditory Response of Word Delay Cue (target 400ms) SUITABLE e.g. 500 ms Speeded Lexical Decision Task YES or NO Beep!

  6. 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

  7. Previous Work: Suffixed Words Derivational suffixes: -ness(20) -less (16) -able (30) -ity (16) Inflection: -ed (30) Matched as closely as possible for length, base and surface frequency

  8. Previous Work: Fillers: - 40 monomorphemic words -nonwords: 40% (25 % of those with some morphological structure)

  9. RT and Percentage Errors by Delay Condition

  10. 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)

  11. 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…

  12. Derivational suffixes: -ness(40) -less (60) -able (60) -ity (60) Inflection: -ed (60) Matched as closely as possible for length, base and surface frequency

  13. 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

  14. 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

  15. RT and Percentage Errors by Delay Condition

  16. -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!) -block design makes -Early sensitivity to morphological structure -Differences in processing for linguistically different suffix types

  17. 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

  18. Future Directions - High accuracy suggests that this task can be performed even faster – further investigation of error effects • Use a wider range of suffixes • Further manipulation of fillers/strategic effects

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