This talk will discuss examples of deficient vision due to morphological, functional and cognitive deficits. A number of unexpected and often glaring instances will be discussed of how we can be unaware of what we are missing in our visual world. Among them are the physiological blind spot, which corresponds to the optic disk that is devoid of photoreceptors and therefore would be expected to produce a large hole in our visual field; transient blindness during photochemical adaptation, which renders us temporarily “blind” when we change from a bright environment to a dark environment and vice versa; inattentional blindness, when we dramatically miss out on events in our visual field, such as a gorilla walking across the room; and change blindness, when major changes in a scene of two pictures presented consecutively go unnoticed.
In addition to these deficits in normal vision there are deficits resulting from pathology. Examples are retinal and cortical scotomata, when large holes in the visual field should occur, but are invisible due to filling-in; visual neglect, when a large region such as a hemifield is ignored, causing us to bump into obstacles; color blindness, when certain hues are not seen because of one or more types of photoreceptors are missing on the retina; face blindness, when faces cannot be recognized because of a genetic defect or, more often, stroke. In blindsight, the opposite is the case: patients can navigate and successfully point towards invisible targets using the extrastriate pathway although they are cortically blind.
In most cases, we are unaware of these “blind spots” present in our daily lives; just think of retroblindness, the very large area behind us, which we take for granted but do not see. Thus, although it is true that often we see more than meets the eye, there are many examples when we see less, although typically we are unaware of it.
Literature
Breitmeyer, B.: The many ways we cannot see. Oxford University Press 2010