- Visual neglect is a neuropsychological condition in which, after damage to one hemisphere of the brain is sustained, a deficit in attention to and awareness of one side of space is observed. It's defined by the inability of a person to process and perceive stimuli on one side of the body or environment.
- Hemispatial neglect results most commonly from strokes and brain unilateral injury to the right cerebral hemisphere, causing visual neglect of the left-hand side of space.
- A stroke affecting the right parietal lobe of the brain can lead to neglect for the left side of the visual field, causing a patient with neglect to behave as if the left side of sensory space is non-existent. If someone with neglect is asked to draw a clock, their drawing might show only the numbers 12 to 6, or all 12 numbers might be on one half of the clock face, with the other half distorted and blank.
- Neglect not only affects present sensation but memory and recall perception as well. A patient suffering from neglect may also, when asked to recall a memory of a certain object and then draw said object, draw only half of the object.
- Some forms of neglect may also be very mild, for example, in a condition called extinction where the ipsilesional stimulus impedes perception of the contralesional stimulus. They can detect a single stimulus presented to their left visual field, but fail to detect the same stimulus when another stimulus is presented to the right of it
Milan Cathedral experiment
Neglect is an attentional problem - there is no visual deficit and no motor deficit. It is reduced by attentional manipulators.
It also affects imagined space - Bisiach & Luzzatti 1978 - Milan cathedral experiment
- In the experiment, neglect patients had to describe a fimilar scene. They had to imagine themselves on the church steps of the cathedral, and describe the view.
- They neglected the left.
- They were then told to imagine themselves facing the cathedral, they then neglected a new left side, which they did not neglect before.
Therefore, it is not a sensory-motor problem.
Inattentional blindness, also known as perceptual blindness, is a psychological lack of attention that isn't associated with any vision defects or deficits. The term was coined by Arien Mack and Irvin Rock in 1992.
It is further defined as the event in which an individual fails to recognise an unexpected stimulus in plain sight. When it simply becomes impossible for one to attend to all the stimuli in a given situation, a temporary blindness effect can take place as a result, where individuals fail to see objects or stimuli that are unexpected and even salient.
A classic study that demonstrated inattentional blindness asked participants whether or not they had noticed a gorilla walking through the scene of a visual task they'd been given.
Change blindness is a perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer fails to notice it. For example, observers often fail to notice major differences when shown an image while it flickers off and on again. People's poor ability to detect changes has been argued to reflect fundamental limitations of human attention.
It is often measured by flicker paradigms: an image and an altered image are switched back and forth with a blank screen in the middle. This procedure is performed at a very high rate, and observers are told to click a button as soon as they see the difference between the two image.
This method of studying change blindness helped researchers discover 2 important findings. The first being that it usually takes a while for individuals to notice a change, even when they are being instructed to look for a change. The second finding is that changes towards the middle of a picture are noticed at a faster rate than changes on the side of a picture.
Attentional blink is a phenomenon where observers will often miss relevant input if it occurs too soon after a previous target.
It is typically measured using rapid serial visual presentation (RSVP) tasks, where participants often fail to detect a second salient target occurring in succession if it's presented between 180-450ms after the first one
Shapiro et al (1994): proposed the interference theory to explain attentional blink. In this model, attentional blink occurs because of an out of place item which is selected out of the series because of the interference within the items in the series. Shapiro proposes that the amount of interference increases or decreases with the length of series.