ResearchBlogging.org Colour blind monkeys are fine at foraging

Fruit foraging may not be the “killer app” for colour vision, according to research published in this month’s issue of PLOSOne [1].

Researchers from Japan, Canada, New Zealand and the UK studied wild black-handed spider monkeys in Santa Rosa National Park, Costa Rica. They used genetic screening to identify nine individuals with full colour vision, and 12 that were red-green colour blind.

Spider monkeys spend 80-90% of their foraging time feeding on fruit. The researchers found that the red-green colour blind monkeys were just as efficient at finding edible fruit as their full-colour vision counterparts.

The researchers measured the colour profile of the fruits and the background foliage and found that the difference in luminance between the two was large enough to show when ripe fruit was present. “The advantage of red-green color vision in primates may not be as salient as previously thought and needs to be evaluated in further field observations,” said the authors.

Technicolour dreams

In the early 20th century results from surveys of dream imagery showed that very few people reported dreaming in colour. However results that date from before the 20th century, and from the 1960s onwards, show the opposite: that colour dreaming is common [2].

In a landmark study in 1942 by Warren Middleton, 71% of college sophomores said that they rarely or never dreamt in colour. When Eric Schwitzgebel replicated the study in 2003 he found that only 17% of students claimed to rarely or never dream in colour.

Eva Murzin from the University of Dundee, Scotland, collected dream data from volunteers that either grew up with predominantly black and media or that did not. Participants were asked to keep a diary of their dreams, or to fill in a questionnaire at a later date.

The results, to be published in the journal Consciousness and Cognition, showed that people over 55 reported a higher proportion of dreams in black and white than those under 55.

The study also showed that, whilst all participants could remember coloured imagery better than back and white imagery, the older participants were better able to recall the details of dreams in black and white than the younger volunteers.

Murzin said: “This result can be interpreted in two ways: either people who claim to have greyscale dreams but have not had experience with such media are simply mislabelling poorly recalled colour dreams or people with early black and white media access misremember the presence of colour in their dreams more easily than people without such experience. This second option could be linked to different expectations and beliefs about dreaming.”

Older brains work differently

Learning to solve visual reasoning tasks like Raven’s progressive matrices is not just a matter of honing existing activity. The parts of the brain used to solve these problems change as we get older [3].

Raven's Progressive Matrix Example
An example problem similar to Raven’s Progressive Matrices, from Wikimedia Commons.

In research to be published in an unpcoming issue of Brain and Cognition, scientists studied the brain activity of 8-19 year-olds solving these types of puzzles. Although children of all ages did equally well on the tests fMRI cans showed that younger children tended to have higher activity in areas of the brain associated with slow, effortful thought. Older participents showed activation consistent with faster, more efficient reasoning.

The study suggests that faster visuospatial reasoning is not the result of brain areas learning to operate more quickly and efficiently. Rather, different brain areas take over as children get better at a task.

[1] Chihiro Hiramatsu, Amanda D. Melin, Filippo Aureli, Colleen M. Schaffner, Misha Vorobyev, Yoshifumi Matsumoto, Shoji Kawamura, Sean Rands (2008). Importance of Achromatic Contrast in Short-Range Fruit Foraging of Primates PLoS ONE, 3 (10) DOI: 10.1371/journal.pone.0003356

[2]E MURZYN (2008). Do we only dream in colour? A comparison of reported dream colour in younger and older adults with different experiences of black and white media Consciousness and Cognition DOI: 10.1016/j.concog.2008.09.002

[3] P ESLINGER, C BLAIR, J WANG, B LIPOVSKY, J REALMUTO, D BAKER, S THORNE, D GAMSON, E ZIMMERMAN, L ROHRER (2008). Developmental shifts in fMRI activations during visuospatial relational reasoning Brain and Cognition DOI: 10.1016/j.bandc.2008.04.010

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