Lecture 8 - Visual Selective Attention + Feature Binding

When do we notice more?

When do we notice more?

When we're paying attention = attention helps us pick out information we want

What does the visual attention domain act as according to Posner (1980)?

Spotlight = items inside spotlight are selected + processed further + items outside don't receive much processing

Define orienting?

Movement/alignment of physical and mental resources towards a region of space = act of all living things e.g. animals and plants

What is used to test orienting of attention in a lab according to Posner (1980)?

Spatial cueing task = demonstrates how attention works in a spatial manner

What mechanisms does the spatial cue task reveal?

Mechanisms of orienting = how selective attention is allocated

What happens to the targets in valid trials?

Appear in same location as the cue = where your attention was first directed

What happens to the targets in invalid trials?

Target appears in different location from cue = different place from where your attention was directed

What does attention facilitate?

Processing (perception) of visual information

Difference between information processed in valid trials vs invalid trials?

Valid processed faster than invalid = shows attention orients around the visual scene like a spotlight

What does attending to a location in space facilitate?

Processing of events in that spatial location

Define overt orienting?

Movement of sensory receptors (eyes) to the location of an external stimulus

Define covert orienting?

Alignment of mental resources to an external stimulus which can be involuntary e.g. stimulus-driven, exogenous or voluntary e.g. top-down, endogenously

What did Banich, M.T. (1997). example show for neuropsychological evidence?

Bill had unilateral neglect:

- Brushed teeth on right side only

- Shaved stubble on right side only

- Didn't see bill on left side of table

Nothing wrong with his eyes = couldn't attend to left visual field = damage to right parietal lobe

What is a test used to see if there's damage to the parietal lobe on a certain side of the brain?

Presented with paper with horizontal lines = have to dissect the line at different locations across the paper

What happens in the replication drawing task as you move up the severity of unilateral neglect?

Drawings get worse + more to one side

6 unilateral neglect symptoms?

- No sensory damage e.g.. no blindness.

- Can't orient (move attention) to one half of the visual field

- Visual, auditory and tactile neglect have been documented

- Bumping into objects and people in the left side

- May fail to groom the left side of their body or eat the left side of what is on the plate

- Voluntary attention and movement to the 'neglected' (left) side is possible but does not always occur naturally

What can neglect inform us about?

How selective attention is allocated

What happens if the brain region that cares about the way that we deploy attention in space becomes damaged?

Can no longer attend to that region of space = need that spatial aspect of attentional selection in order to organize visual input + allow us to select objects/ items for attending to in space

Define vision?

Process of de-constructing the image of what we see into tiny pieces of information, processed in different areas of the brain

What does the striate cortex (V1) receive?

Receives all visual input from Lateral Geniculate Nuclei and begins processing of colour, motion & shape

What does the V3 deconstruct?

Depth

What does the V4 deconstruct?

Colour

What does the V5/MT deconstruct?

Motion

What does the LO deconstruct?

Shape

Define motion agnosia a (Zihl et al., 1983)?

Loss of ability to detect motion while perfect at all other visual tasks, following damage in area MT

Define cerebral achromatopsia?

Loss of the ability to see colours but intact detection of all other visual properties, following damage in area V4

What is the binding problem in vision?

We perceive the whole object, not fragments of shapes, colours and moving patterns = confusion in how we combine the different features into the percept of a single object

What mechanism solves the binding problem + example?

Attention e.g. searching for something

What can the visual search paradigm help us understand?

How attention can assist perception by being the glue binding the different feature representations together into objects

What do participants look for in a feature search?

Target that does not share any of its features with the distractors = RTs are fast regardless of how many distractors there are in the visual field

What do participants look for in a conjunction search?

Target that shares features with the distractors = RTs in this case are increased with increasing number of distractors

Examples of how the target can differ among other items by a single feature? (3)

- Red among yellow

- Tall among short

- Ball in the haystack

What happens when the target is defined by a unique feature?

Doesn't matter how many other items are in the display e.g. we quickly find the teacher in the nursery regardless of how many children they are surrounded by

Why are some searches hard in a conjunction search?

Target shares features with other items in the visual field = attention has to get there to spot target after exhaustively inspecting other locations = more the items in the display (set) we need to search through the more time is needed to find our target e.g. it takes longer to find our teacher friend in a room at a Teacher's Conference if there are a lot of other people

What theory did Treisman & Gelade (1980) discover?

Feature Integration Theory (FIT)

Describe the first stage of the visual search: pre-attentive stage?

Basic visual features are detected + processed and available in parallel = no need for attention

Describe the second stage of the visual search: attentive stage?

Different visual features are bound together to form an object

Example of the pre-attentive stage?

If task is to find something red = only colour map needs to be accessed = each feature map is created without attention in parallel = set size won't matter in search times and the object is identified quickly

What is the attentive stage also known as?

Serial process = demands attention = acts like a glue, binding the features together

Example of the attentive stage?

- Task is to find a red triangle = need to consult two maps = colour & shape

- Requires attention + more time

- Each feature map is consulted without attention, in parallel, but binding of different maps together (so that we can find the red triangle) is a serial process + takes time and attention = is slower + the more items in the array the longer we take

Why is no attention required if a target object can be found on the basis of a single basic feature (shape or colour)?

Feature (disjunction/pop out search) = targets are found faster because they differ from distractors on basis of a single feature

What does the FIT say is needed for?

To bind different features of the same object together

Why are conjunction targets found slower?

As they differ from distractors on basis of how the features are conjoined together = if target object is a combination of two or more features then attention is required

What process requires focused attention?

Joining features together to create a coherent visual percept

How does target-distractor similarity affect visual search?

More features the distractors share with the target = slower the search

How does size of the array affect visual search?

More the distractors = slower the search for a conjunction target (although set size makes little difference in time taken when carrying out a feature search)

What happens before attention focuses on a location?

Visual features and the identity of the target are not bound together (not grouped)

What happens when attending to a location in correct conjunctions?

Features present at that location are correctly bound (grouped) together to a single object

What happens when attending to a location in illusory conjunctions?

Without focused attention features from different objects may be combined randomly forming 'illusory conjunctions'