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Common Visual Preference for Curved Contours in Humans and Great Apes

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Gerardo Gómez Puerto

on 4 December 2015

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Transcript of Common Visual Preference for Curved Contours in Humans and Great Apes

Image by Tom Mooring
2AFC task
with minimized semantical content
common visual preference for curved contours in humans and great apes
what we know
what we don't know
take home message
Further research
not the result
of learning!
n = 9 (7 chimpanzees & 2 gorillas) trained in the use of a touch screen

36 x 2 pairs of real objects at 84ms
M = 50.5; SD = 2.4; t(8)=.62, p=.276; 95% CI: 48.7-52.3

same stimuli under a free time presentation
M = 53.3; SD = 3.1; t(8)=3.15, p=.007; 95% CI: 50.9 - 55.6
Captive apes trained to use a touch screen from the Wolfgang Köhler Primate Research Center in Leipzig
Minimal changes to 2AFC task
Chimps were rewarded, in a quasirandom manner 50%, percent of the trials. The randomization was set so that there wouldn’t be more than 2 trials in a row with or without reward
5 sessions per condition
2 Alternative Forced Choice Task (2AFC)
Target pairs (sharp vs round contour) or distractor pairs (same contour, different meaning)
We avoid using terms in the semantic field of taste or preference when instructing the participants in the task
Instead, they are prompted to select one of the images for it to be shown once again, enlarged
In this way, we attempt to simulate an approach- avoidance scenario

n = 20 students 36 x 2 pairs of images depicting real objects at 80ms
M = .581; SD = .136; t = 2.6902, p = 0.0145; 95% CI = .518 - .646

n = 29 students 36 x 2 pairs of images depicting real objects at free time
M = .533; SD = .142; t = 1.232, p = .228; 95% CI = .478 - .587
our design finds preference for curvaure
under free time in apes, but not in humans
n = 21 (of 23) rural Mexicans
n = 27 (of 29) students from the UIB
preference in humans is higher with shorter presentations. at 500ms, top-down judgements
might be influencing reaction time
40ms: n = 15 (of 16)
80ms: n = 20
150ms: n = 15 (of 20)
300ms: n = 15 (of 20)
500ms: n = 13 (of 17)
Free time: n = 27 (of 29)
chimpanzees share most of the features of
our visual system and might only differ in
perceptual grouping
8 shapes, with varying degrees of complexity, regularity and symmetry, were created in their round and sharp versions
Then, all the 4 possible global-local combination of these were built, being paired so to compare curvature and global-local interaction, resulting in 7 pairs per each of the 8 forms, ammounting to a total of 56 stimuli shown twice

we wanted to further test whether some effect could be found manipulating the global local interaction and facilitating or not the
gestaltic closing of the pattern
chimpanzees: n = 7
students from UIB: n = 29
no significant effects were found

n = 24 students from UIB: when global and local share the same contour there is an effect of preference for curvature

n = 32 students from UIB: there might be an effect of preference when the global pattern is round, regardless of the local features, when facilitating closing
n = 18 students from the UIB at 80ms
n = 35 (of 38) students from the
UIB at 40ms
what is in fact curvature, and why is it relevant?
which mechanisms modulate preference for curvature, and how do they interact with higher cognition
which kind of ecological pressure would account for the emergence of the preference for curvature
curvature interacts with valence
preference for curvature
might be influenced
by cultural trends
or/and it might be innnate
sharp contours are
presentation time
does matter
expertise might
interact with preference
for curvature
most research reports effects of preference for curvature with long testing times

amygdala activations has not been detected with longer presentation times

approach-avoidance designs doesn't result in positive findings with long presentation times
eye tracking
working hypothesis
curved stimuli, being preferred, will be fixated faster
in the earlier perceptual stages, curved stimuli will be looked at longer
on the whole, adult humans might not look at curved stimuli longer than at sharp ones, but apes certainly will

sharp stimuli being perceived as a threat will be fixated earlier
curved stimuli, being preferred, will be looked at longer

Set up
participants are shown a pair of images in a screen set approximately 60-70 cm from their eyes
a tobii eye-tracker placed underneath the screen records the movements of the eyes
when working with apes, a juice dispenser is used so that they keep facing the screen
experimental design
each trial consists on a oriented response cue being shown for 90ms, in order to direct the attention to the center without promting a fixation that could cause inhibition of return
it is followed by a target pair being displayed for 3 secs
afterwards, a binary noise screen shown for 1 sec "resets" the visual buffer
finally, a blank screen shown for 1 sec mitigates the impact of afterimages
contour curvature is relevant for both humans & big apes
as a trend, curved contoured objects are chosen more often than sharp ones
they are also fixated faster and looked at longer
in the case of adult humans, elements such as culture or personality seem to affect this trend once higher congnition gets into the mix
our most precise field of vision is constrained from the 2º visual arc of the fovea to the 5º of the parafovea
it's generally agreed that fixations are a reliable proxy of different cognitive phenomena
most eyetrackers use the corneal reflection of infrared light, together with different algorithms, to accurately pinpoint the eye's position
what's a fixation and what's a saccade is a somewhat arbitrary/pragmatic decision
...but this doesn't always work!
The stimuli consisted in 20 pairs of images depicting real objects, plus 20 pairs showing novel, abstract patterns
n = 26 (12 chimps, 6 bonobos, 7 orangs & 1 gorilla) already familiar with the setup. the 40 pair of images were spread along 4 sessions
as predicted, apes seem to have fixated curved stimuli faster, and looked at it longer
lots of missing data (~50%)
n = 19, 20 pairs of images depicting real objects and 20 of novel patterns
as predicted, curved stimuli was fixated faster and looked at longer during the first 500ms

something you have to know about humans
is that we do have quite a bias towards the
left field of vision!
gerardo gómez-puerto
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