Psychology 251: Attention (UVic)

What is Attention?

Given limited capacity to process competing

options, attentional mechanisms select, modulate,

and sustain focus on information most relevant for

behavior.

Problem

How to allocate limited resources in the service of

behavior

Importance

We need to prioritize information so we do not waste

time and energy on irrelevant efforts

Challenge

How to balance the need for selective focus with the

need to handle new situations as they arise

Exogenous Source of Attention

In the environment, reflexive, automatic, "bottom-up"

Eg. a clap, flash

Endogenous Source of Attention

In the mind, voluntary, intentional, "top-down"

Eg. a goal, desire

External Target of Attention

Sensory information, in the environment

Eg. Spacial location, Object

Internal Target of Attention

Mental representations, in the mind

Eg. A Memory, Imagery or Plan

What are the different types of Attention?

Overt vs. Covert

Transient vs. Sustained

Selective vs. Divided

Overt Attention

Shifting attention from one place to another by moving the eyes

Covert Attention

Occurs when attention is shifted without moving the eyes, commonly referred to as seeing something "out of the corner of one's eye"

Transient Attention

Momentary focus on something

Sustained Attention

The ability to maintain attention to a selected stimulus for a prolonged period of time

Selective Attention

The ability to focus on only one stimulus from among all sensory input

Divided Attention

Concentrating on more than one activity at the same time

What is the Source of Attention?

The cause of directing ones attention

When does Attentional Selection occur?

As sensory input is transformed into percepts (once we make sense of it, we go to a motor response)

What is the Dichotic Listening Task?

Method for studying selective attention. Subjects wear headphones with two different audio streams. Have to repeat one stream and ignore the other.

Dichotic Listening Study, Cherry 1953

Subjects could report existent of message in unattended ear, could report the gender of the speaker but could not report the content. Lead to Broadbent Filter Model

Broadbent's Filter Model

Our cognitive systems are only capable of processing one meaningful input at a time, so when there are multiple inputs, our system is strained and must quickly switch back and forth between inputs. Known as all-or-non filtering because only attended message makes it through to higher processing

Dichotic Listening Study, Moray 1959

The subject could report change in the gender of the speaker and could report change in pitch of tone. Could not report a word repeated many times, however reported hearing their own name in unattended ear

Dichotic Listening Study, Gray and Webbeburn 1960

The subject was told to attend to the left ear, but in the middle they would switch the message to the right ear and then back. Subject were able to put message together without fully attending

Treisman's Attenuation Theory

Instead of complete selective filter, have an attenuator - weakens but doesn't eliminate input from unattended ear. Then some gets to perceptual processes, so still assign meaning to stuff in unattended ear, just not high priority. Then switch if something important. "Leaky filter"

Dichotic Listening Study, McKay 1973

Attended ear is given ambiguous sentences "they were throwing stones at the bank" unattended ear participants heard related words. "river" or "money"subjects were then tested, and had to chose a sentence that was closest to the meaning of the message. The meaning of the word in the unattended ear affected the participants choice

Late Selection Model

Proposed by McKay that attentional selection occurs later on closer to the motor response.

What is the correct model of Attentional Selection?

Early vs. Late selection can be chosen based on situation and approach. Attention is applied by top-down modulation

What is an ERP?

Event Related Potential: The measured brain response that is the direct result of a specific sensory, cognitive or motor event

Electroencephalogram (EEG)

An amplified recording of the waves of electrical activity that sweep across the brain's surface. These waves are measured by electrodes placed on the scalp. Measures surface electric fields generated by post-synaptic potentials in dendrites of neurons

What are ERP's dependant on?

How the neurons are organized, this makes it difficult to know where the signal is coming from

How are ERP's created?

When a stimulus is perceived the subject pushes a button, signals from the EEG are averaged for only the points where the stimulus is present. Plotted with the negative up

ERP's can be used to form a

Surface distribution of ERP wave form through time

Attentional Stream Paradigm

A paradigm used in attention research in which two or more segregated series of stimuli are presented in parallel and subjects selectively attend to one of the series to perform a task

What was the effect of attention on auditory ERP's in the brain stem with the attentional stream paradigm?

There was no affect.

What was the effect of attention on auditory ERP's on midlatency potentials with the attentional stream paradigm?

Difference in the attended and unattended signals was observed - showing there was an effect

What was the effect of attention on auditory ERP's with the late waves with the attentional stream paradigm?

There is a large difference between the attended and unattended ear. The attended sounds caused a larger response in the brain

Poser Orientating Task

Used to measure manual and eye-movement reaction times to target stimuli and assess attention. Subject maintains focus on central point, and cues occur telling them to pay attention to either side. Sometimes cues are valid 80% sometimes invalid 20%

What is the source of Attention in the Posner Task?

Endogenous because your brain tells you to attend to one side or the other based on cues

What is the target type in the Posner Task?

External because you are looking to something in the outside world not your own mind

What type of Attention is used in Posner Task?

Covert: no eye movements since you are fixed on target

Transient: momentary focus

Selective: not focusing on multiple things

In a ERP what do the P1 and N1 stand for?

The first neural responses that are observed after a visual stimulus.

What is the visual attentional stream paradigm?

Similar to spatial cueing (like the posner task) but with sustained attention, to one side more than the other. Had larger peaks at attended location vs. unattended location.

Attention affects Reentrant Activity

Attention affects different stages of brain activity

The location of visual attentional effect: V1, V2, V3, V4, can be seen in the brain during MRI, what is shown with this?

Increased activation due to attention occurs in all the visual areas. This means that attention has widespread effects throughout the visual pathway and increases the firing of neurons

What were the results of the functional MRI study on spatial attention effects in the LGN?

There was increased activation in the area representing the attended and decreased activation in the unattended.

In the MRI there was also activation shown in the thalamus. Why?

Effects of attention start early in time but they are also pervasive throughout the brain.

Describe the experiment by Moran and Desimone (1985) on the visual attention of V4 neurons

Animal is presented with a central fixation to the left of the receptive field of V4. There are two stimulus bars within the receptive field. One is preferred (red bar) and unpreferred (green bar). Animal attending to effective stimulus has a stronger firing of the neurons, compared to animal attending to the ineffective. however the neuron fires in both cases.

Orientation Tuning Curve

A function relating the firing rate of a neuron to the orientation of the stimulus. Attention causes GAIN (multiplicative scaling), but no change in feature selectivity.

If the signal enhanced by attention is low contrast, what is the result?

Small response, small change ie. if stimulus is too small neuron won't respond at all

If the signal is medium contrast then the result is?

Medium response, big change ( or difference between attended and unattended)

If the signal is high contrast (ie really bright), what are the results?

There is a big response but small change. If stimulus is really bright then less attention is needed so the difference between attended and unattended isnt as big as medium contrast.

Higher Level Visual Attention Study

A study that involved visual attention to objects, attending to faces or scenes and told participants to attend to one and ignore the other. Activity was greatest when attending to faces.

What were the results of this study?

Attention occurs in low level visual areas all the way up to high visual processing like the fusiform facial area.

Attention can have effects less than _______________ after stimulus onset

100 ms

Where does attention modulate neural activity?

In brain areas for locations and objects

Attention increases _________________between brain areas.

Neural Synchronization.

What does attention synchronization between brain areas mean?

Attending to a stimulus is associated with increased synchronization between all areas of the brain that are processing the stimulus together.

Unilateral (Hemispatial) Neglect

⦁ A deficit in perceiving and responding to stimulation contralateral to damaged hemisphere

⦁ A deficit of attention

⦁ Most often, left-side neglect after damage to right parietal lobe

Neglect cannot be explained by

Primary sensory or motor disturbance - patients can still see the stimulus they just aren't paying attention to it.

The study on neglect in milan italy found that patients have neglect in their

Visual imagery from memory

What are the multiple reference frames of neglect?

Spatial, Object-based

Spacial neglect

A disorder caused by damage to the left parietal lobe typified by behaviors indicating the individual's inability to respond to the left part of their body and or external environment

Object-based neglect

Person ignores left half of all objects

What is the attentional control network?

Regions involved in endogenous and exogenous shifts of attention

Change Blindness

Changes in a picture or scene over time are not immediately apparent if not attended to