Chapter 7 – Attention and scene perception
Attention: Very large set of selective processes in the brain. Since we handle all inputs at
once, the nervous system has created special mechanisms that are able to restrict processing
to a subset of things/ideas/moments/ in time.
There are 5 different types of attention that are not mutually exclusive.
1. External vs internal attention. External attention is the attention to stimuli in the
world. Internal attention is our ability to select one process over the other.
2. Covert vs overt attention. Overt attention is directing a sense organ on the stimulus-
for example fixating the eyes on a single word. Covert attention is pointing your eyes
on one page while directing attention to a person of interest off to the left.
3. Divided attention – reading the book and continuing to be aware of the music playing
in another room.
4. Sustained attention – watching the pot to notice the moment it starts boiling is
5. Selective attention – the ability to pick one or a few out of many stimuli.
Reaction time: a measure of the time from the onset of a stimulus to the response.
Cue: like a hint or stimulus that indicates where something will be. A cue decreases reaction
time because you are paying attention and know exactly where to look.
Stimulus Onset Asynchrony: The time between the onset of one stimulus and the onset of
another. As SOA increases, peripheral cues increase. However symbolic cues take longer to
work because we need to do some work to interpret the colored dot cue.
As we shift our gaze, the point of fixation sweeps across the intervening space. Saccadic
suppression does inhibit this though. We have no direct way of measuring the location and
extent of attention. It has also been suggested that attention is not moving from point to
point in the brain as a spotlight would.
Visual search: search for a target in a display containing distracting elements.
Target: the goal of a visual search
Distractor: any stimulus other than the target.
Set size: the number of items in a visual display
Efficiency: the ease at which we can work out way through a display. Feature searches are
efficient. Its often harder to locate an object when its not 3d and has no orientation in depth
Many searches are inefficient: when the target and distractions in a visual search contains the
same basic features. Searching for arbitrary objects is not efficient. Serial self terminating search: searching from item to item and ending when it’s found.
Feature search: search for an object with a specific attribute,. Example color
Salience: the vividness of a stimulus relative to its neighbors.
Parallel search: a search in which multiple stimuli are processed at the same time.
More specifically –
Feature Searches are Efficient
- Feature search: search for a target defined by a single attribute, such as a salient color or
- Salience: the vividness of a stimulus relative to its neighbours
- Parallel search: a search in which multiple stimuli are processed at the same time
Many Searches Are Inefficient
- When target and distractors in a visual search task contain the same basic features, search is
- Serial self-terminating search: a search from item to item, ending when a target is found.
- some searches are inefficient, meaning that each additional item in the display imposes a
significant cost on the searcher
In Real-World Searches, Basic Features Guide Visual Search
Guided search: a type of search in which attention can be restricted to a subset of possible
items on the basis of information about the target items basic features.
Conjunction search: search for a target with two or more attributes present. Ex. Red vertical
target among red horizontal and blue vertical distractors.
In Real-World Searches, the Real World Guides Visual Search
Scene-based guidance: based on the understanding of our scenes that help us find objects in
Binding problems: the challenge of trying different attributes of visual stimuli. Ex. Color,
motion, orientation which are handled by different brain circuits, to the appropriate objects
so that we perceive a unified object. Ex. Red, vertical, moving right
Feature integration theory: a theory of visual attention which holds that a limited set of basic
features can be processed in parallel preattentively, but that other properties, including the
correct binding of features to objects require attention.
Illusory conjunction: we might be sure we say a green H but it was a false combination of
features. It is an erroneous combination of two features in a visual scene,
Proto-object: a loose collection of unbound features. Such as size, color etc which will be a
recognizable object once attended. Rapid Serial visual presentation: an experimental procedure where stimuli appear in a stream
at one location at a rapid rate.
Attentional blink: our ability to visually attend to the characters in RSVP sequence were
temporarily knocked out even though our eyes were wide open. You catch one fish, you cant
immediately catch a second fish, there are some time costs.
Repletion blindness: a failure to detect the second occurrence of an identical letter, word,
or picture in a rapidly presented stream of stimuli when the second occurrence falls within
200-500 miliseconds of the first.
Attention could enhance neural activity:
Fusiform face area: different parts of the brain are important in the processing of faces. A
region of extrastriate visual cortex activated by human face.
Parahippocampal place area: activated by images or places than by other stimuli.
The best evidence for a change in the fundamental preferences of a neuron comes from
studies of its preference in space – that is its size and shape of neurons receptive field.
Reynold and Heegers “normalization” theory: the current response of a neuron is the
product of that’s neurons built in receptive field and the effects of attention. This products
must then be normalized by neural suppression.
Response enhancement: an effect of attention on the response of a neuron in which the
neuron responding to an attended stimulus gives a bigger response.
Sharper tuning: an effect of attention on the response of a neuron in which the neuron
responding to the attended stimulus responds ore precisely
DISORDERS OF VISUAL ATTENTION
Visual field defect:a portion of the visual field with no vision or abnormal vision due to a
damage in the vi