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

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