1. Presented by Espen Sjoberg
Effects of foraging-related stimuli on object location memory and perceptual search in the hunter-gatherer theory
Presented by Espen Sjoberg
University of Essex
Co-authors:
Geoff Cole, PhD
Luke Cannon, BSc

2. What is hunter-gatherer theory?
Proposed by Silverman & Eals (1992).
Attempts to explain sex differences in spatial abilities from an evolutionary perspective.
In Middle Pleistocene era (ca years ago), a labour division existed where men were hunters and women were gatherers, and from this different cognitive abilities have evolved.

3. Evidence from: Mental Rotation
Men outperform women on this task.
Study of over participants across 40 countries yielded an effect size of
d = 0.48 (Silverman, Choi, & Peters, 2007)
Meta-analysis of 35 studies found
d = 0.67 (Voyer, Voyer, & Bryden, 1995)
controlled for science education, gaming experience, and Lego experience (Peters et al., 1995)
performance is mediated by higher motivation in men to do well (Estes & Felker, 2012)

4. Evidence from: Object Location Memory (OLM)
Women outperform men at this task.
Meta-analysis of 86 studies gave an effect size of d = 0.27 (Voyer, Postma, Brake & Imperato-McGinley, 2007).
Study of over participants across 40 countries yielded an effect size of d = 0.31 (Silverman, Choi, & Peters, 2007)

5. Female OLM advantage relies on experimental conditions
Factors that reduces the female advantage:
Removing the relative component (Postma et al., 1998)
Abstract items (Rahman, Bakare, & Serinsu, 2011)
Reducing difficulty (Sjoberg, 2012)
Distance (Saucier, Lisoway, Green, & Elias, 2007)
Presentation/Trial interval (Honda & Nihei, 2009)
Ecological validity (Stoet, 2011; Ianchini et al., 2005; Cherney & Ryalls, 1999)
Masculine items (Voyer et al., 2007)
In addition, female rats outperform males in object-location memory, despite absence of language and labour division (Saucier et al, 2008).
(To any brave researchers out there I recommend testing lions!)

6. What about foraging-related stimuli?
Very little research has looked into the effect of foraging related stimuli on memory (e.g. fruit):
Women remember the location of plants better than men (Neave, Hamilton, Tildesley, & Pickering, 2005)
Men and women in the Hadza tribe do not differ in OLM performance between animal and fruit stimuli (Cashdan, Marlowe, Crittenden, Porter, & Wood, 2012)
But:
If the relative component is removed, women outperform men on OLM with “fruit on trees” stimuli (Krasnow, Truxaw, Gaulin, New, Ozono, Uono, Ueno and Minemoto, 2011)

7. Our study
Before any conclusions can be drawn with respects to animal and fruit stimuli in terms of hunter-gatherer theory, the usual female advantage with relative OLM should first be demonstrated.

8. Experiment 1 Object-location memory task
(conventional, relative component)
3 stimuli categories:
Neutral Animal Fruit
(non-foraging)

9. Experiment 1 PREDICTIONS
Hunter-Gatherer Predicts:
Women better at neutral stimuli than men
Women’s performance should improve with fruit stimuli relative to neutral stimuli
Men’s performance should improve with animal stimuli relative to neutral stimuli

10. Experiment 1 RESULTS N = 76 p = .049 Correctly positioned pictures
Stimuli type

11. Experiment 2 Reaction-time experiment
Identify fruit or animal in 20-item array
Timed YES/NO responses

13. Experiment 2 PREDICTIONS
Hunter-Gatherer Predicts:
Women faster at fruit stimuli than animal stimuli
Men faster at animal stimuli than fruit stimuli
Men and women both would employ search strategies during labour division, but for different reasons and for different stimuli!

14. Experiment 2 RESULTS N = 53 p = .17, ns Reaction time (ms)
Stimuli type

15. Conclusions Results only partially support hunter-gatherer theory.
With OLM the usual female advantage with neutral stimuli was observed, with an effect size in line with previous research.
The female advantage was abolished with fruit and animal stimuli.
Men and women did not differ in search speed regardless of stimuli.

16. Post-hoc speculation
Both fruit and animal stimuli may carry equal evolutionary weight, but for different reasons:
Animals:
Animals have potentially dangerous trajectory changes and so we should have increased processing with animal stimuli (New, Cosmides, & Tooby, 2007)
Fruit
Possible that fruit carry equal evolutionary weight between both sexes due to its function as a highly used food source.
Would suggest that any mechanism for fruit stem from a longer evolutionary history than suggested by hunter-gatherer theory

17. These hypotheses may help to explain why fruit/animal performance do not differ. However:
Why did men improve their performance with animals/fruit in OLM and not women?
OLM
Target search

18. Post-hoc speculation: OLM
It may be that women’s performance cannot improve beyond a certain threshold.
In other words, in relative OLM women already hold an advantage over men due to their verbal abilities, and this advantage cannot further increase.
However, if this was true then removing the relative component should show increased performance with fruit and animal stimuli with both sexes, but this does not occur (Krasnow et al., 2011)

19. Final comment
Speculative explanations may account for some of the results, but additional experiments are needed to fully understand the observed outcomes. Regardless of why these effects were observed, we cannot conclude that the results are supported by the hunter-gatherer theory.

20. Acknowledgements Conference sponsors: HBES EPS
Sincere thanks to Rachael Wilner, and also Eva Sjoberg
Thank you!
THE END

21. Male
Female
Cohen’s d
Fruit (RT)
1153 (407)
1122 (319)
0.09
Animal (RT)
1240 (407)
1098 (229)
0.45
Fruit (No. correct)
8.9 (1.3)
9.2 (1.0)
-0.27
Animal (No. correct)
8.9 (1.4)
9.1 (0.9)
-0.18
Fruit FP
2.3% (0.43)*
0% (0)*
0.81*
Animal FP
0.9% (0.29)
2.1% (0.42)
-0.33

22. Supp.