Fluid intelligence and the many faces of executive function Helen Davis School of Psychology Murdoch University Acknowledgements: Catherine Leong

Fluid intelligence Raw reasoning ability Biological basis Closely aligned with g Increases until early adulthood Is there a simple, information-processing explanation for differences in fluid intelligence?

Executive Function Active selection of behaviour from alternatives Active selection of behaviour from alternatives Strategy generation Strategy generation Inhibition Inhibition Attention switching, goal maintenance, working memory Attention switching, goal maintenance, working memory Monitoring & modifying performance (Rabbitt, 1997) Monitoring & modifying performance (Rabbitt, 1997) Frontal lobe related Frontal lobe related Relation to fluid intelligence –Development (Bjorklund & Harnishfeger, 1989; Davis & Anderson, 2001) Is EF general or task-specific?

The Stroop Colour-Word Task Conditions –Congruent: REDBLUE GREEN –Neutral:XXXXXX XXXX –Incongruent:BLUE GREENRED Selectively attend to ink colour (not word) Interference effect = incongruent – neutral Facilitation effect = neutral - congruent

The Stroop Colour-Word Task Blocked trials GREENREDBLUE XXXXXXXXXX GREENREDBLUE Mixed trials XXXXGREENBLUE XXXREDBLUE XXXGREENRED

An accidental finding… Blocked trials: –Interference effect decreases with age (7-10 years) –Facilitation effect - no change Mixed trials: –Interference effect no change –Facilitation effect decreases with age (7-10 years) –Lack of interference / facilitation correlation

Some enlightenment from Kane & Engle (2003)? Working memory (WM) capacity and Stroop task (adults) –Blocked trials: Interference effect (time cost) greater for low WM Selective attention only? –Mixed trials: No interference (time cost) difference between WM groups Greater facilitation effect (time benefit) Selective attention + goal maintenance?

Research Questions Does Stroop facilitation reflect goal neglect? –Is Stroop facilitation related to goal neglect on separate task? –Is Stroop facilitation related to working memory capacity? –Is Stroop facilitation distinct from Stroop interference? Which, if any, of these executive function measures predict developmental change in fluid intelligence?

Method Participants: 7-year-olds (n = 34) –mean age = 7.4 ( ) –18 boys, 16 girls –18 boys, 16 girls 10-year-olds (n = 40) –mean age = 10.2 ( ) –26 boys, 14 girls

Tasks Raven’s Standard Progressive Matrices –Group test (fluid intelligence – raw score) Digit span –forward (short-term memory) –backward (working memory)

Stroop task –Individual, computer administered –3 colour (red, green, blue) –Conguent, Incongruent, Neutral –3 blocks of 36 mixed trials –Measured reaction time (RT) Switching task –Computer administered (goal maintenance/neglect)

Switching Task Stimuli

Switching Task Procedure Red task Plant or animal? ‘Z’ for plant ‘/’ for animal 64 trials Green Task Small or large? ‘Z’ for small ‘/’ for large 64 trials Dual Task Alternating 4 trials red, 4 trials green 64 trials total

Results Raven’s Progressive Matrices

Stroop Task Reaction Time Facilitation effect F(1,68) = 52.62*** Interference effect F(1,68) = *** Facilitation x Age F(1,68) = 3.03, p=.08 Interference x Age F(1,68) = 7.19** Age F(1,68) = 19.02***

Digit Span Age –Forward F(1,68) = 13.58*** –Backward F(1,68) = 28.54***

Switching Task Switch cost F(1,66) = *** Switch cost x Age F(1,66) = 6.95** Age F(1,66) = 40.50***

p <.05; p <.07; n.s. Task Intercorrelations AgeRaven’sStroopDigit SpanSwitch Facil.Interf.FDSBDS Age Raven’s Facil Interf FDS BDS.-.34 Switch.

Stepwise Linear Regression – Predicting Fluid Intelligence from Executive Function PredictorBetatsig R2R2R2R2 B-Digit Switch cost Facilitation Interference

In answer to research questions… Does Stroop facilitation reflect goal neglect? –Is Stroop facilitation significantly related to goal neglect on separate task? NO –Is Stroop facilitation significantly related to working memory capacity? NO –Is Stroop facilitation distinct from Stroop interference? YES

Which, if any, of these executive function measures predict: –Developmental change in fluid intelligence Working memory (BDS) Goal neglect (switch cost) Selective attention (interference effect) Whatever the facilitation effect is(!)

Conclusions The Stroop facilitation effect cannot be easily interpreted as an measure of goal neglect. Executive functions are multiple. The development of fluid intelligence may be the result of the summation of different executive functions maturing relatively independently.