Primates possess an incredible ability to detect faces in their peripheral vision at remarkable speeds, thanks to a newly identified brain circuit. Researchers have found that rhesus macaque monkeys (Macaca mulatta) can categorize a blurry peripheral image as a face or an object in under 40 milliseconds, long before turning their gaze for a detailed look. This discovery sheds light on the brain’s ancient mechanisms for rapid face detection.
The superior colliculus, an evolutionarily ancient part of the brain, plays a crucial role in this rapid face detection. This ‘shortcut’ circuit transfers information from the eyes to an early visual cortex and then to the midbrain. Unlike the more familiar face recognition circuit, which involves newer parts of the primate visual cortex and takes longer, this shortcut is incredibly fast but can only detect face-like objects in the periphery.
While humans recognize familiar faces at the center of their vision in about 380 milliseconds, this ancient circuit in macaques operates much quicker for peripheral detection. Researchers are exploring whether similar neurons in the superior colliculus perform the same function in humans. This circuit is known to help young children follow faces and react to emotional stimuli.
Experimental Findings
Experiments conducted by researchers at the US National Institutes of Health (NIH) involved scanning the brains of two macaques while showing them various images. The images were placed just outside the central visual field, making them indistinct to known face-recognition circuits. The study revealed that 140 neurons in the superior colliculus responded most strongly to monkey faces in the periphery.
Detection Speed of monkeys could distinguish between faces and non-faces just 30 milliseconds after an image was shown. By 50 milliseconds, the accuracy of discrimination reached 80%, and it peaked at 92% by 90 milliseconds.
Animate vs. Inanimate Objects superior colliculus discriminated between animate and inanimate objects with only 75% accuracy, 65 milliseconds after the image was shown.
Implications for Face Recognition Development
These findings suggest that higher-order cortical areas are necessary for consciously interpreting objects, whereas face-like features trigger immediate midbrain responses. This might explain why newborns fixate on faces despite lacking developed ‘face patches’ in their visual cortex, and why some primates can quickly orient towards other faces.
Researchers aim to investigate if this face-preference circuit exists in humans. Understanding this circuit could reveal how the brain’s advanced facial recognition processes develop and may provide insights into conditions like autism. Deficits in this face preference in the superior colliculus could play a role in autism spectrum disorders, making this an important area for further study. The study was published in Neuron.
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