Individual Differences in Lexical Processing and Cerebral Asymmetries Christine Chiarello*, Suzanne Welcome*, Laura K. Halderman*, Janelle Julagay*, Ronald Otto**, Christiana M. Leonard^ *University of California, Riverside **Computerized Diagnostic Imaging Center, Riverside ^ University of Florida, Gainesville Supported by NIDCD #006957

Biological Substrates for Language Project Do individual differences in cortical anatomy have behavioral significance?

Correlation of Composite Task Asymmetry and Planum Temporale Asymmetry (Chiarello, et al., 2004)  Reaction time: r = +.50  Accuracy r = +.42  Reaction time: r = +.50  Accuracy r = +.42

Consistency of Asymmetry  Extent to which asymmetry varies from norm across brain regions, or across tasks  Z-score each regional and task asymmetry  sd of z-scores across regions or tasks indicates degree of consistency  Extent to which asymmetry varies from norm across brain regions, or across tasks  Z-score each regional and task asymmetry  sd of z-scores across regions or tasks indicates degree of consistency

Correlation of Consistency (sd) of Anatomical and Behavioral Asymmetries (Chiarello, et al., 2004)  Based on sd of z-scored asymmetries  r = +.52  Association of variability for anatomical and behavioral asymmetry  Based on sd of z-scored asymmetries  r = +.52  Association of variability for anatomical and behavioral asymmetry

Chiarello, et al. (2004). Neuropsychology, 18,

Consistency may indicate buffering of cortical development  Inconsistent persons may have less buffering  Random genetic and/or environmental influences may deflect asymmetries from modal pattern of development  Inconsistent persons may have less buffering  Random genetic and/or environmental influences may deflect asymmetries from modal pattern of development Waddington’s Epigenetic Landscape

Consistency of Behavioral Asymmetries  Are consistent individuals different from inconsistent individuals in other ways?  Is consistency associated with an advantage/disadvantage for language processing?  Do consistent and inconsistent groups differ in degree or direction of asymmetry?  Are consistent individuals different from inconsistent individuals in other ways?  Is consistency associated with an advantage/disadvantage for language processing?  Do consistent and inconsistent groups differ in degree or direction of asymmetry?

Biological Substrates for Language Project (N = 110) MeanRange Age22.1 yrs18-34 Verbal IQ Performance IQ Woodcock Reading Mastery Test Percentile: Word Identification52.6%15-89 Word Attack51.9%5-98 Passage Compreh.69.4%8-99

Divided Visual Field Tasks:  Word Naming 1, 2  Nonword Naming  Lexical Decision  Masked Word Recognition  Semantic Decision  Verb Generation  Category Generation  Word Naming 1, 2  Nonword Naming  Lexical Decision  Masked Word Recognition  Semantic Decision  Verb Generation  Category Generation Pronounce word Pronounce nonword Word/nonword discrimination Forced choice recog of forward & backward masked word Natural/manmade discrimination Produce verb related to stimulus noun Produce category member to category name Pronounce word Pronounce nonword Word/nonword discrimination Forced choice recog of forward & backward masked word Natural/manmade discrimination Produce verb related to stimulus noun Produce category member to category name

Determining Consistency of Asymmetry:  Z-score RT asymmetry for each task  Compute sd of each person’s asymmetries across tasks  Rank order sample by this sd  Top quartile (N = 27) represents most consistent persons, bottom quartile (N = 27) represents most inconsistent persons  Z-score RT asymmetry for each task  Compute sd of each person’s asymmetries across tasks  Rank order sample by this sd  Top quartile (N = 27) represents most consistent persons, bottom quartile (N = 27) represents most inconsistent persons

Most ConsistentMost Inconsistent # Males1412 Hand Preference SES Verbal IQ111 Performance IQ Word ID % Word Attack % Passage Comp % Hand Perf Speed9.8 sec Corr of Word Nam 1 & 2 Asymmetry

Group Differences - RT Across LVF & RVF

Group Differences - Central VF Trials WNam2VerbGen

Composite Task RT Asymmetry

Consistency of Asymmetries is a Continuum More Consistent More Inconsistent More buffered neurodevelopment Less buffered neurodevelopment Slowed lexical access Reduced AsymmetriesIncreased Asymmetries

Kosslyn, et al. (2002): within a biological framework, variation in mental processes is the phenomenon of interest; it is not “noise”