Seeing clearly

Why do we not notice the limitations of our eyes and any time lag in perception? A recent paper by A. Herwig which was reported in ScienceDaily (here) looks at the mechanics of vision.

Only one portion of the retina has detailed vision, the fovea. If we hold our arm out, a bit about the size of a thumb nail, is seen clearly by the fovea. The rest of vision is not sharp. And yet we seem to have clear vision of a much larger area.

This paper puts forward a model that has the memory storing pairs of blurred and detailed images. When there is a blurred object in the visual field (but not in the fovea) it is replaced in the visual system by a detailed image of an object that fits the blurred image coming from the eyes. This is done so quickly that a person never observes the blurred object. These pairings of blurred and detailed objects are being continually updated.

The researchers used a very fast camera to follow a subject’s eye movements. During the extremely fast movements, saccades, from one fixed position to another, they changed the object that would be viewed. The subjects did not see the new object but rather the detailed pairing with the old blurred object.

The experiments show that our perception depends in large measure on stored visual experiences in our memory.” …these experiences serve to predict the effect of future actions (“What would the world look like after a further eye movement“). In other words: “We do not see the actual world, but our predictions.

This give us a clear visual picture that appears correct and immediate.

Here is the abstract (A. Herwig, W. Schneider; Predicting object features across saccades: Evidence from object recognition and visual search; Journal of Experimental Psychology: General (2014) 143-5)

When we move our eyes, we process objects in the visual field with different spatial resolution due to the nonhomogeneity of our visual system. In particular, peripheral objects are only coarsely represented, whereas they are represented with high acuity when foveated. To keep track of visual features of objects across eye movements, these changes in spatial resolution have to be taken into account. Here, we develop and test a new framework proposing a visual feature prediction mechanism based on past experience to deal with changes in spatial resolution accompanying saccadic eye movements. In 3 experiments, we first exposed participants to an altered visual stimulation where, unnoticed by participants, 1 object systematically changed visual features during saccades. Experiments 1 and 2 then demonstrate that feature prediction during peripheral object recognition is biased toward previously associated postsaccadic foveal input and that this effect is particularly associated with making saccades. Moreover, Experiment 3 shows that during visual search, feature prediction is biased toward previously associated presaccadic peripheral input. Together, these findings demonstrate that the visual system uses past experience to predict how peripheral objects will look in the fovea, and what foveal search templates should look like in the periphery. As such, they support our framework based on ideomotor theory and shed new light on the mystery of why we are most of the time unaware of acuity limitations in the periphery and of our ability to locate relevant objects in the periphery.


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