Iowa City, IA, USA. First evidence has emerged that human perceptual processes for facial recognition are present in other vertebrates, a finding that challenges traditional behavioral research and increases the importance of biological traits in the continuing debates over nature vs. nurture.

People count on the human face try to reveal identity and emotional expressions that aid identification and categorization, a trait that can either enhance or impede communication.

Ed Wasserman, a professor of experimental psychology, and graduate student Fabian Soto, both of the University of Iowa (UI), conducted the study and published their findings in the Journal of Vision. Instead of making comparisons with other primates, Wasserman and Soto focused on a species at a greater evolutionary distance, the common pigeon.

General and Adaptive Mechanisms



Human Identity and Emotional Expression. University of Iowa (UI) researchers found that pigeons recognize a human face's identity and emotional expression in much the same way as people do.

The image shows examples of the face stimuli shown to the pigeons in experiments conducted by Fabian Soto and Ed Wasserman.

Click Pic for DetailsComparing the traits and performance of distantly related species is a useful scientific strategy for isolating a specific behavior and determining whether is due to a general perceptual system or the result of a specialized adaptation. If the distantly related species share a remote common ancestor they are more likely to share mechanisms for information processing.

• Survival across diverse environments results from the general mechanisms (e.g., object recognition is general).
  
  
• Adaptive specializations should be present in only one of two distantly related species under comparison (e.g., face recognotion is particular) — unless, of course, convergent evolution of the same processes result from similar evolutionary pressures.

Vision science recognizes that birds compare well with primates because the two groups possess the most advanced biological visual systems. However, it is highly unlikely that birds have evolved a specialized system for the processing of human faces. Any similarities between the two groups are therefore the likely result of conserved evolutionary mechanisms.

• Previous studies assessed the ability of birds to categorize human faces and showed that pigeons and crows can do it according to gender and emotion. Moreover, they transfer this learning to novel visual images.
  
  
• Color and shading were shown to be particularly important in the gender studies. Pigeons use information near the eyes and chin to discriminate between male and female faces, using information near the mouth to distinguish between happy and neural faces.

The Mix of General and Adaptive

The authors of the current study found that even pigeons recognize a human face's identity and emotional expression in much the same way as people do. The authors found that both specialized and general processes are likely to be involved when people recognize other human faces, requiring empirical verification of both before coming to firm conclusions.

Pigeons were shown photographs of human faces that varied in the identity of the face, as well as in their emotional expression — such as a frown or a smile.

• Experiment 1 was preparatory, a study of whether pigeons can perceive the similarity structure of stimuli that vary along the dimensions of human face identity and emotional expression.
  
  Pigeons, like humans, were observed to perceive the similarity among faces sharing identity and emotion.
  
  
• Experiment 2 was designed to task the pigeons with categorizing the photographs according to only one of these dimensions and to ignore the other.
  
  The pigeons found it easier to ignore emotion when they recognized face identity than to ignore identity when they recognized face emotion.

Observations and New Directions

The researchers studied pigeons in this project because they have excellent vision and are not close evolutionary relatives of humans. Pigeons do not have a specialized system for face processing, but they still show similarities to people when they are trained to recognize human faces. The simplest interpretation of these similarities is that they result from general recognition processes shared by both species.

"This asymmetry has been found many times in experiments with people and it has always been interpreted as the result of the unique organization of the human face processing system." Soto said. "We have provided the first evidence suggesting that this effect can arise from perceptual processes present in other vertebrates.

"The point of the project is not that pigeons perceive faces just as we do or that people do not have specialized processes for face perception. Rather, the point is that both specialized and general processes are likely to be involved in peoples' recognition of faces and that the contributions of each should be carefully determined empirically," he added.

It has been a popular practice among behavioral researchers in perception and cognition to speculate about specialized mechanisms without offering convincing empirical data to support their ideas. The new findings could make scientists reconsider their assumptions about how uniquely human cognitive processes might interact with more general processes in complex tasks such as face recognition.

"We hope that our research will prompt other researchers to conduct more comparative work to assess their claims about the evolution of uniquely human perceptual and cognitive processes," Wasserman said.

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<style type="text/css"><!--.quote {width:400px; padding: 6px; border: solid 1px #456B8F; font: 11px helvetica, verdana, sans-serif; color: #222222; background-color: #ffffff}.quote a {font: 13px arial, serif; color: #003399; text-decoration: underline}.quote a:hover {color: #FF9900; }//--></style><div style="float:left;padding:5px;"></div><div class="quote"><a href="../biology/29592-some-face-perception-not-uniquely-human" target="_blank">Some Face Perception Not Uniquely Human</a><br/>Wednesday, 13 April 2011<div align="right" style="width:400px"><p style="text-align:right;"><a href="/" target="_blank">TS-Si.org</a></p></div></div>

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