Hemispheric Asymmetries: Early and Mid Level Visual Processing Lynn - PowerPoint PPT Presentation

Hemispheric Asymmetries: Early and Mid Level Visual Processing Lynn C. Robertson

Delis, Robertson, & Efron Neuropsychologia, 1986

S S S S S S S S S S S S S S S S S S S S S S S S

Global/Local

Standard Left Hand Right Hand YYYYYYYYY Y Y Y Y Y (From Delis, Kramer & Kiefner 1988)

Attention Manipulation: 50/50 G/75 L/75 Is there an H or S? Distractors: A E

Divided Attention

E E H H H H E E H E E E E H H H E E H E E H H H H

50/50 G/75 Reaction Time L/75 Local Global Target

Robertson, Lamb & Knight J of Neuroscience, 1988 Participants: 11 patients and 9 normal controls N = 5 N = 6

Robertson, Lamb & Knight J of Neurosciences, 1988 50/50 G/75 L/75 RHD LHD Local Global Local Global Target Level Target Level

Focused Attention

Locally Directed: Is the Small Letter and H or S? H H S S H H S S H H H H S S S S H H S S H H S S Presented Centrally and Peripherally

Globally Directed: Is the Large Letter and H or S? H H H H H H H H H H H H H H H H H H H H H H H H Presented Centrally and Peripherally

Lamb, Robertson & Knight Neuropsychologia, 1989 300 200 Peripheral Reaction Time (msec) Central 100 0 -100 -200 Control Left temporal- Right temporal- parietal parietal

Studies showing hemispheric asymmetry for global/local processing: • Neuropsychological: • Electrophysiological: – Delis et al. , 1986 – Han & Chen, 1996 – Lamb et al. , 1989 – Han et al. , 2000 – Robertson & Delis, 1986 – Heinze et al. , 1998 – Robertson & Lamb, 1991 – Robertson et al. , 1988 • Functional imaging: – Robertson, Lamb, M. R., & – Fink et al., 1997 Zaidel, E., 1993 – Han et al., 2002 – Martinez et al., 1997 – Weissman & Woldorff, 2005

LOW HIGH

DFF Theory ( Ivry & Robertson, Two Sides of Perception 1998 ) Power RH LH Low High Frequency Left Hemisphere Right Hemisphere Power Power Relatively Low Relatively High Relatively Low Relatively High Frequency Frequency

Categorical vs. Coordinate (Kosslyn) Coordinate : Right hemisphere precise spatial relations Categorical : Left hemisphere rough spatial relations Coordinate task : Is the dot near or far from the line? Categorical task : Is the dot above or below the line?

Left Eye Left Hemisphere Right Eye Right Hemisphere

RT RH * LH * Categorical Coordinate • Categorical Task: Faster for LH • Coordinate Task: Faster for RH

DFF account • LSFs facilitate coordinate (near/far) task -- RH • HSFs facilitate categorical (up/down) task -- LH

Removing LSFs should harm RH: Coordinate CB(HSF) BB

Okubo & Michimata, 2002 BB CB RH RT * LH * * Categorical Coordinate Categorical Coordinate • Eliminating LSF affects in coordinate task

LSF BB

Okubo & Michimata, 2004 BB LSF RH * RT * LH * Categorical Coordinate Categorical Coordinate • Eliminating HSFs affects categorical task

DFF theory has done pretty well Can it be applied to more complex stimuli? e.g. Faces

Left Right 5 µ V -5 N170 Bentin, et al., 1996

Face Detection: N170 • N170: well-investigated index of relatively early processing of faces P8 µ V mushrooms flowers 6 houses lions tools 2 traffic signs textures -2 N170 faces -6 ms 0 100 200 300 400 Itier, R.J. & Taylor, M.J. (2004)

Anastasia Flevaris Shlomo Bentin

Task: Respond to flowers Low spatial frequency (LSF) 0.9 cycles/degree 4 cyncles/face Hi spatial frequency (HSF) 5 cycles/degree 22 cycles/face

LSF cutoff 0.9 c/deg ) HSF cutoff 5 c/deg )