Perceptual Processes ch 7

Attention Definition

• Attention involves the selective processes in the brain.
• Selective attention restricts processing to a subset of possible stimuli.

Flavors of Attention

• External attention involves attending to stimuli in the world.
• Internal attention involves attending to one line of thought over another or selecting one response over another.
• Overt attention involves directing a sense organ toward a stimulus.
• Covert attention involves attending without giving an outward sign.
• Divided attention involves splitting attention between two different stimuli.
• Sustained attention involves continuously monitoring some stimulus.
• Humans aren't good at multitasking because the brain is not actually developed for multitasking.
• Attention requires allocating resources to decide what to attend to and process.
• Sustained attention or vigilance tasks require monitoring the environment over time for a target.
• People cannot actually attend to two or more things simultaneously; rather, they switch quickly between different things.

How to Study Attention

• Reaction time (RT) is a measure of time from a stimulus onset to a response.
• A cue is a stimulus that may indicate a subsequent stimulus.
• Cues can be valid, invalid, or neutral.
• Stimulus onset asynchrony (SOA) is the time between the onset of one stimulus and another.

Cues

• Simple probe detection experiments involve the Posner cueing paradigm.
• Cues can be valid or invalid.
• Reaction time is shorter on valid cue trials.
• Reaction time is longer on invalid cue trials.
• Exogenous cues are located at the desired location of attention.
• Peripheral cues capture attention automatically and shift it to the desired location.
• Endogenous cues are located at the current location of attention.
• Symbolic cues must be learned and require interpretation to shift attention.

Benefit of a valid cue (ms)

• Individuals respond faster to peripheral cues

Inhibition of Return (IOR)

• IOR is the relative difficulty in getting attention to move back to a recently attended location.
• During searches, IOR stops you from getting stuck continually revisiting one spot.
• IOR prevents people from wasting time looking at the same location over and over again.

Theories of Attention

• The "spotlight" model restricts attention in space and moves it from one point to the next, giving areas within the spotlight extra processing.
• The farther apart two items are, the longer it takes to shift attention between them.
• The "zoom lens" model allows the attended region to grow or shrink depending on the area being processed.
• As the spotlight gets larger, it also gets dimmer.
• The larger the area of attention, the less attentional resources each item in the area gets.

Visual Search

• Visual search involves looking for a target in a display containing distracting elements.
• The target is the goal of a visual search.
• A distractor is any stimulus other than the target in visual search.
• Set size refers to the number of items in a visual search display.
• The more distractors, the more challenging the search usually is.
• Pop-out search involves a target that always pops out and is easy to find.
• Conjunction search involves a target that is slightly harder to find due to more similar distractors.
• Spatial configuration search involves finding a target in various spatial orientations, making it harder.
• The efficiency of visual search is the average increase in RT for each item added to the display.
• It is measured in terms of search slope (ms/item)
• The larger the search slope, the less efficient the search.
• Some searches are efficient with small slopes, while others are inefficient with large slopes.
• Feature searches are efficient and define a target by a single attribute, such as color or orientation.
• Salience is the vividness of a stimulus relative to its neighbors.
• Parallel refers to the processing of multiple stimuli at the same time in visual attention.
• Inefficient searches involve serial self-terminating search, where the search goes from item to item, ending when a target is found.
• Guided search restricts attention to a subset of items based on their characteristics.
• Conjunction search involves searching for a target defined by the presence of two or more attributes.
• There is no single feature that defines the target, instead it is defined by the co-occurrence of two or more features.
• Scene-based guidance uses scene understanding to find specific objects.
• An anchor object, a relatively large object, provides information about the location of other objects.
• Scene grammar involves rules about where things can be within a scene; violations of these rules tend to capture attention.
• Scene syntax refers to what is considered normal for a scene.

Binding Problem

• The binding problem ties different attributes of visual stimuli, which are handled by different brain circuits, to the appropriate object so we perceive a unified object.
• Preattentive processing of basic features can occur in parallel
• Feature integration theory states that a limited set of basic features can be processed in parallel preattentively, but other object features require attention.
• The preattentive stage involves processing before selective attention is deployed, while color and orientation are processed preattentively.
• Illusory conjunctions are erroneous combinations of two features in a visual scene.
• They provide evidence that features are represented independently and need to be correctly bound together with attention.

Rapid Serial Visual Presentation (RSVP)

• RSVP is an experimental presentation of stimuli in a stream at one location at a rapid rate (typically about eight per second) and is used to study the temporal dynamics of visual attention.
• Attentional blink is the difficulty perceiving and responding to the second of two target stimuli and the 2nd target is often missed if it appears within 200 to 500 ms of the first target.
• A mental set is the conscious selection of attentional focus.
• Brain areas show increased activation when attending to objects processed in those areas like the fusiform face area and parahippocampal place area.

Brain Activity

• Attention cells could be changed in three ways
• Response enhancement
• Sharper tuning
• Altered tuning
• Attention to a specific part of the visual field causes neurons coding those locations to have increased activity and enhances activation in those areas being attended.
• Early processing gathers basic feature information about stimuli.
• Features are combined on a priority map, with attention moved to the most active spot.

Attention Disorders / Scene Perception

• Visuospatial neglect is a disorder of attention where the individual fails to attend or respond to one half of visual space despite normal vision and cognitive function.
  • It's caused by damage to the parietal lobe.
  • It occurs contralateral to the damaged hemisphere, most severely following right parietal lobe damage.
• Failures in attention often occur, examples include:
  • Illusory conjunctions (incorrectly combining features of separate stimuli).
  • Action slips (inattention to a task leads to unintended actions).
• Magicians take advantage of this by misdirecting attention.
• Some tasks require more attention than others, where if more resources are needed for one task, less is available for others.
• Two pathways exist for scene perception: the selective pathway, and the nonselective pathway.
• Selective pathway permits the recognition of one or very few objects at a time and passes through the bottleneck of selective attention and a reentrant processing pathway.
• The selective pathway gathers information from all sensory inputs, sending it to a sensory buffer, here some sensory info enters conscious processing while other info is filtered out, until information passing through the filter enters conscious awareness
• The nonselective pathway contributes information about the distribution of features across a scene and the "gist” of the scene and does not pass through the bottleneck of attention, using a feed forward pathway.
• The non-selective pathway computes ensemble statistics, which are the average and distribution of properties (e.g., orientation or color).
• It computes scene gist and spatial layout.
• Spatial layout describes the structure of a scene (e.g., enclosed, open, rough, smooth).

Importance of Memory

• Memory for objects and scenes is overall good.
• A task where subjects looked at 2500 objects in a training phase and chose which of two objects they had previously seen was performed in 2008.
• For objects of different types, they preformed the task with 92% accuracy.
• For objects of the same category, they performed with 88% accuracy.
• For the same objects in different states, they preformed with 87% accuracy.
• While overall good for details, it also suffers from "change blindness", which is the failure to notice a change between two scenes.
• This failure demonstrates how humans do not encode and remember as much of the world as originally thought.
• Humans tend to focus on the gist of the image and not the specific details.
• The perception of what is seen is often driven by a person's expectations of what they "should" be seeing.
  • This leads to failures of attention and accidentally filtering out certain details.
• Finally, inattentional blindness is a failure to notice or report a stimulus that would be easily reportable if it were attended.