Esta noticia nos la envía el lector Anthony Rodríguez directamente desde el MIT (Instituto de Tecnología de Massachussetts), y al final ponemos un enlace a la versión completa en inglés, pero he aquí el resumen...

Según publica Anne Trafton de la Oficina de Prensa de MIT, los científicos siempre han tenido la curiosidad de por qué se hace tan difícil para nosotros el poder reconocer una cara en una foto en negativo, ya que después de todo una foto "positiva" (o "relevada" como se decía antes) y una negativa contienen exactamente la misma información y en los mismos lugares, salvo que los colores son "inversos" (es decir, lo negro es blanco, y lo blanco es negro).

Ahora, Ming Meng del MIT y Sharon Gilad del Weizmann Institute of Science en Israel creen haber dado con la respuesta, o al menos parte de esta.

El truco, dedujeron estos investigadores, es que los humanos tenemos una fuerte afinidad a los ojos de las personas, y una característica que defina el concepto de una cara de manera bastante fuerte en nuestras mentes es el contraste de color oscuro y claro que existe en los ojos de una persona y el resto de la cara. Se podría decir que en prácticamente cualquier circunstancia de imagen, esta es casi una constante, en donde los ojos se ven mas oscuros que el resto de la cara.

Así que para comprobar esto hicieron un experimento en donde a varias personas les presentaron 3 tipos de fotos de personas famosas, con el objetivo de que las identificaran. El primer tipo de fotografía era una imagen normal ("en positivo"), la segunda una imagen en negativo, pero la tercera era especial... Esta tercera foto era un negativo pero que en los ojos se había restaurado el positivo.

Según los resultados esta modificación en el tercer tipo de imágenes cambió por completo la capacidad de reconocer las caras en las personas.

Lo mejor de todo es que esto no es una simple curiosidad, sino que tiene fines prácticos. Por ejemplo, hoy sabemos que los autistas en muchos casos tienen problemas reconociendo las caras de personas, y la razón ahora se especula no es que vean "en negativo", sino que se ha comprobado que estas personas se concentran en ver las bocas de las personas en vez de los ojos.

Esto significa que sabiendo este dato, sería posible crear algún tipo de tratamiento para autistas que tienen problemas reconociendo personas.

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Nota Extendida...
Research probes why we have difficulty recognizing faces in photo negatives

Anne Trafton, News Office
March 13, 2009

Humans excel at recognizing faces, but how we do this has been an abiding mystery in neuroscience and psychology. In an effort to explain our success in this area, researchers are taking a closer look at how and why we fail.

A new study from MIT looks at a particularly striking instance of failure: our impaired ability to recognize faces in photographic negatives. The study, which appears in the Proceedings of the National Academy of Sciences this week, suggests that a large part of the answer might lie in the brain's reliance on a certain kind of image feature.

The work could potentially lead to computer vision systems, for settings as diverse as industrial quality control or object and face detection. On a different front, the results and methodologies could help researchers probe face-perception skills in children with autism, who are often reported to experience difficulties analyzing facial information.

Anyone who remembers the days before digital photography has probably noticed that it's much harder to identify people in photographic negatives than in normal photographs. "You have not taken away any information, but somehow these faces are much harder to recognize," says Pawan Sinha, an associate professor of brain and cognitive sciences and senior author of the PNAS study.

Sinha has previously studied light and dark relationships between different parts of the face, and found that in nearly every normal lighting condition, a person's eyes appear darker than the forehead and cheeks. He theorized that photo negatives are hard to recognize because they disrupt these very strong regularities around the eyes.

To test this idea, Sinha and his colleagues asked subjects to identify photographs of famous people in not only positive and negative images, but also in a third type of image in which the celebrities' eyes were restored to their original levels of luminance, while the rest of the photo remained in negative.
Subjects had a much easier time recognizing these "contrast chimera" images. According to Sinha, that's because the light/dark relationships between the eyes and surrounding areas are the same as they would be in a normal image.

Similar contrast relationships can be found in other parts of the face, primarily the mouth, but those relationships are not as consistent. "The relationships around the eyes seem to be particularly significant," says Sinha.

Other studies have shown that people with autism tend to focus on the mouths of people they are looking at, rather than the eyes, so the new findings could help explain why autistic people have such difficulty recognizing faces, says Sinha.

The findings also suggest that neuronal responses in the brain may be based on these relationships between different parts of the face. The team found that when they scanned the brains of people performing the recognition task, regions associated with facial processing (the fusiform face areas) were far more active when looking at the contrast chimeras than when looking at pure negatives.

Other authors of the paper are Sharon Gilad of the Weizmann Institute of Science in Israel and MIT postdoctoral associate Ming Meng, both of whom contributed equally to the work..

The research was funded by the Alfred P. Sloan Foundation and the Jim and Marilyn Simons Foundation.

autor: josé elías