While it does not feel like it, human vision is rather limited: we only see clearly in a small region around the current line of sight. Visual information in the periphery is highly degraded. For example, when scanning your book shelves for a title of interest, you only have access to detailed visual information, such as the text on the spine, where you are currently looking. To view the titles and authors of surrounding books, you would have to shift the line of sight by moving your eyes (and, for large gaze shifts, the head).
To overcome this limitation of the visual system, humans actively sample their environment during brief periods of stable fixation. During a fixation you have to do at least two things: analyse the object you are currently looking at (for example, identify whether the currently fixated book is the one you were looking for), but also to select candidate objects in the periphery for an eye movement for future inspection (for example, based on the colour of the covers).
A great deal of research has shown the humans frequently have great difficulty performing multiple perceptual tasks at the same time. When a complex shape has to be identified in central vision, there may be a cost in the detection or identification of peripheral visual events such as the appearance of a new object. This phenomenon is known as ‘tunnel vision’ and may impede human performance in a variety of domains (imagine making sense of a complex route shown on your GPS display while driving).
Research carried out by Dr Casimir Ludwig from Bristol’s School of Experimental Psychology in collaboration with the University of California Santa Barbara, has shown that the detailed analysis of the object in central vision occurs in parallel with the selection of the next fixation location in peripheral vision. Moreover, they found that both ‘tasks’ are performed independently. That is, variation in the difficulty of central object analysis does not influence the extraction of information from the periphery.
The highly efficient way in which we perform both tasks presumably reflects their importance and ubiquity in everyday vision: looking in the right place at the right time is the starting point of other, more complex, forms of human behaviour.
The study is published in the Proceedings of the National Academy of Sciences.
‘Foveal analysis and peripheral selection during active visual sampling’ by Ludwig, C.J.H., Davies, J.R., & Eckstein, M.P. in Proceedings of the National Academy of Sciences