Temporality vs Spatiality in Vision

With the exceptions of colour and brightness, most visual features are primarily spatial. Colour and brightness are primary aids in the determination of these spatial properties. All properties have the potential to vary across time, so there can be a temporal aspect to all of these features.

But the fact that only a small region of the visual field has enough resolution to resolve fine details means that there is an implicit temporality in the ways that the visual image is constructed. Image details are sensed because the eye is rapidly moving back and forth to generate a sense of edges. We 'see' an image with a wider field of detail that the retina is capable of providing because of larger scale movements of the eye. All this movement at the core of the process of seeing is masked out to provide a stable sense of our surroundings. So in a sense, part of the job of our visual system is to make time disappear.

On the other hand, the movement of the fovea is used in reading text and music to crate an artificial flow of time. The movement of the eye over a text or score is not gradual and continuous, but full of leaps and backward steps. We do not sense this movement as jerky because of the above-mentioned stabilizing effect of visual perception. It seems that higher frequency temporal effects are masked, but the lower frequency sense of progression through time is sustained. There is a 'steadicam' like effect that smoothes out the small rapid motions and creates the sense of a gradual progression.

It is also notabe that the spatial and temporal sensitivities of the eye vary across the retina. The periphery of the retina is much more sensitive to motion than the fovea, but it much less sensitive to detail. So there is a sort of gradient from fovea to periphery with a transition from spatial bias to temporal bias.

It may also be significant that a sense of the overall scene is not resolved in vision until at least 1/10 of a second after the fact. The eye has a more immediate sense of local features like the orientation of edges, general stereoscopic depth, spatial frequency and movement. This might mean that rapidly fluctuating information is best presented in terms of these local features.