Imageability Effects on Sentence Judgments by Right Brain-Damaged Adults

1. Imageability Effects on Sentence Judgments by • Right Brain-Damaged Adults • Lisa G. Lederer 1, April Gibbs Scott 1, Connie A. Tompkins1,2, Michael W. Dickey 1 • University of Pittsburgh; 2. Center for the Neural Basis of Cognition • Pittsburgh, P.A. USA

2. INTRODUCTION & OVERVIEW • Image generation has often been assumed to be a right hemisphere function. • Many recent studies, however, have localized image generation to the posterior left hemisphere (see Farah, 1995, for a review). • This study sought to clarify the relationship between right hemisphere damage (RHD) and image-generation ability using a stimulus set developed by Eddy and Glass (1981). • The performance of adults with and without RHD was compared on true/false items whose solution did or did not require imagery generation.

3. PARTICIPANTS • 34 adults with unilateral RHD (confirmed by CT or MRI) due to CVA • 38 healthy controls • Monolingual native speakers of American English • Pre-morbid right-handedness • RHD’s performed significantly poorer than healthy control group on: • Peabody Picture Vocabulary Test-Revised (Dunn & Dunn, 1997) • Behavioural Inattention Test (Wilson, Cockburn, & Halligan, 1987) • Visual Form Discrimination (Benton, Sivan, Hamsher, Varney, & Spreen, 1994) • Judgment of Line Orientation (Benton, Hamsher, Varney, & Spreen,1983)

4. PARTICIPANT DEMOGRAPHICS Characteristics                       RHD (n=34)                         NBD (n=38) Age(years)    Mean (SD)               64.74 (11.57)                       60.45 (9.61) Range                     42-85                             45-84   Gender Male    17                                        19 Female     17           19 Education(years)   Mean (SD)              14.42 (2.96)                          13.95 (2.27)      Range               10-22                12-20 Months post-onset  Mean (SD)              52.91 (50.99) Not applicable Range                    4-167

5. STIMULI & PROCEDURE • 18 High- and 17 Low-imageability sentences, as determined by naïve raters, from Eddy & Glass (1981) (matched for noun frequency, mean auditory verification RTs, truth agreement, and comprehensibility) • 36 filler stimuli similar in structure • Participants received extensive orientation and practice until reaction time stabilized • Stimuli presented auditorily via a notebook computer through supra-oral earphones • Participants responded true/false on manual two-button box • Were encouraged to respond as quickly as possible • Completed over 3 sessions • High-imageability sentences classified as motor/visual or visual-only by 3 raters with > 80% inter-rater reliability for post-hoc analysis

6. LOW-IMAGEABLE • There are six days in a week. • Geology is the study of living matter. • Middle age comes after old age. • The best student is at the bottom of the class. • A country has windows. • There are three human sexes. • Spring is a month. • A novel is shorter than a novelette. • The introduction follows the story. • Salt is used less often than pepper. • The prince will one day be queen. • A pound is heavier than a ton. • Most watchdogs are Bulldogs. • Animals are stuffed by a toxicologist. • Geology studies the history of mankind. • A father buys children. • The US government functions under a three party system.

7. HIGH-IMAGEABLE VISUAL ONLY MOTOR/VISUAL • A row boat comes to a point in the back. • The symbol for degrees is an apostrophe. • Yellow is darker than orange. • A grapefruit is larger than a cantaloupe. • A stop sign has seven sides. • Tractors have two very large wheels in front. • The letter A is formed with four lines. • The number 9 can be constructed from two circles. • The hot water handle on a sink is on the right. • A right handed hitter places his right side toward the plate. • The accelerator on a car is on the left pedal.

8. RESULTS General Analysis (Two-way ANOVA) • Both groups more accurate on Low- than on High- imageable items (F(1, 71) = 25.02, p < .001) • RHD group less accurate than NBD in general (F(1, 70) = 6.40, p =.014) • Group x Imagery interaction in RT (F(1, 63) = 5.42, p = .023) • NBD group  faster on Low- than High-imageable items (t(33) = 2.44, p =.020). No difference between High and Low items for RHD group (t(30)=1.00, p = .325, ns) Post-hoc Imagery Type Analysis • Group x High Imagery type accuracy interaction (F(1, 70) = 5.71, p =.02) • RHD group less accurate than NBD on visual/motor items • No group difference on visual-only items

9. RESULTS

10. RESULTS

11. DISCUSSION • Differences in RT between stimulus sets (high vs. low imageable) were only seen for the NBD group. • Not due to a speed-accuracy tradeoff or to syntactic differences between stimulus sets (per correlation analyses) • Suggests that RHD disproportionately slows access to “world” knowledge as opposed to imagery-based knowledge. • Consistent with Farah (1995) and others’ assertion that image generation primarily involves the left hemisphere

12. FURTHER DISCUSSION & IMPLICATIONS • Post-hoc analysis of visual-only vs. visual/motor imagery suggests that this relative sparing of visual imagery generation does not extend to motor imagery. • Adults with RHD might rely disproportionately on visual imagery generation processes but not on motor imagery generation processes. • Researchers should consider the distinction between visual imagery and motor imagery generation. • Clinicians should attempt even more fine-grained analysis (i.e. less coarse than “visual imagery generation” and “motor imagery generation”) of clients’ problem areas.

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