Early Time Course Hemisphere Differences in Phonological & Orthographic Processes Laura K. Halderman

1

, Christine Chiarello

1

& Natalie Kacinik

2 1

University of California, Riverside

2

University of California, Davis

Introduction

•Chiarello (2003) has proposed that the cerebral hemispheres use different processing styles for linguistic information •LH - processes information rapidly, quickly moving to a deeper level, discarding initial, more shallow representations •RH - processes information more slowly, maintaining shallow representations of the information, even if no longer relevant •Form-Specific vs Abstract Form (Marsolek et al., 1992) •Word Length effects in RH (Lavidor & Ellis, 2002) •This model did not specifically consider phonological processes in reading •Research on split-brain patients has revealed little evidence for Grapheme-to-Phoneme Conversion processes in RH (Baynes & Eliassen, 1998 & Zaidel, 1985) •GPC processes in the LH have been attributed to speech mechanisms being located in the same hemisphere •Normal population studies have revealed mixed results •Phonology •No evidence for phonology in RH (Khateb et al., 2000; Crossman & Polich, 1988; Rayman & Zaidel, 1991) •Used metalinguistic tasks - Rhyme Judgment •Evidence for bilateral phonological processes (Chiarello et al., 1999; Coney, 2002; Weekes, 1999) •Orthography •Greater orthographic processes in the RH (Crossman & Polich, 1988; Marsolek, 1992) •Orthographic facilitation in RH, but no phonological facilitation (Lavidor & Ellis, 2003)

Lateralized Backward Masking

30 ms

+ XXXX

12 0 m s 30 ms 30 ms

+ boat + BOTE + XXXX

30 ms boat beat Forced Choice Items 4000 ms

•Presentation of target beings initial processing which is interrupted by the pseudoword mask •Similar masks reinstate some of the initial decoded properties of the target and facilitates identification •Pattern mask restricts perception to the initial processed properties of the target and mask •Participants are unaware of the nonword mask

O+P+

boat BOTE

Mask Type Conditions O+P-

boat BOTS

O-P-

boat NENE

Predictions

•Left Hemisphere •LH will show facilitation for orthographic condition at both SOAs •LH will show facilitation for phonological condition at both SOAs •Right Hemisphere •RH will show facilitation for orthographic condition at both SOAs •RH will not show facilitation for phonological condition •However, if phonological processes are slower in the RH, facilitation may occur in the 50 ms SOA

Backward Masking Methods

•Participants •96 Native English speaking undergraduates •Right-handed •Stimuli & Presentation •150 Experimental Trials •Pseudowords matched for orthographic regularity using Bigram frequencies (Mayzner & Tresselt, 1965) •Forced Choice items matched for frequency (Francis & Kucera, 1982) •30 ms & 50 ms SOAs •Each component of the stimuli was presented for 30 ms or 50 ms

Results

1700 1600 1500 1400 1300 1200 1100 1000 900 30 ms SOA - RT - Visual Field X Mask Type 1700 1600 1500 1400 1300 1200 1100 1000 900 LVF/RH RVF/LH

•

LH

•

O+P+ < O+P-

•

O+P- < O-P-

•

RH

•

O+P+ = O+P-

•

O+P- < O-P O+P+ O+P O-P 50 ms SOA - RT - Visual Field X Mask Type LVF/RH RVF/LH

•

LH

•

O+P+ = O+P-

•

O+P- < O-P-

•

RH

•

O+P+ = O+P-

•

O+P- < O-P O+P+ O+P O-P-

Simple Masking Experiment

•A second experiment was conducted using a similar paradigm to compare the effects of the pseudoword mask to a condition with no pseudoword mask •All methods were repeated except no pseudoword appeared between the target and final pattern mask •Only the 30 ms SOA was examined •Participants - 48 Native English speaking, Right-handed undergraduates

Results

No pseudoword condition compared to pseudoword condition - 30 ms 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 NoMask O+P+ O+P O-P LVF/RH RVF/LH

•Significant RVF advantage •NoMask condition interacts with O+P+ and O+P- conditions •No interaction between NoMask conditon and O-P- condition

Conclusions

•When no pseudoword mask is presented, the RVF advantage is equal to the Unrelated pseudoword mask condition •However, when a pseudoword mask sharing relevant orthographic or phonological information is present, the hemispheres differentially use the overlapping information to facilitate target recognition •The LH is benefited most by overlapping phonology at the shortest SOA, while the RH is benefited most by orthography •RH does not show access to phonology, but it does demonstrate greater orthographic facilitation than the LH at this early time course, an effect similar to Lavidor and Ellis (2003) •These results suggest the LH is capable of generating a phonological representation of words very quickly, perhaps automatically •The RH, on the other hand, is capable of generating an orthographic representation very rapidly which stands in contrast to general findings of slower, RH processes (Chiarello, 2003) This research was conducted under the support of the National Science Foundation grant BCS-0079456, granted to the second author.