cognition, brain and consciousness: an introduction to cognitive neuroscience edited by bernard j....

Cognition, Brain and Consciousness: An Introduction to Cognitive NeuroscienceEdited by Bernard J. Baars and Nicole M. Gage2007 Academic Press

Chapter Attention and Consciousness

“Millions of items … are present to my senses which never properly enter into my experience. Why? Because they have no interest for me. My experience is what I agree to attend to … each of us literally chooses, by his ways of attending to things, what sort of a universe he shall appear to himself to inhabit”

William James, 1890, Principles of Psychology

Attention is often thought of as a spotlight, aiming to select some part of the world for conscious access


Chapter Outline

1.0 Introduction

2.0 A distinction between attention and consciousness

3.0 Experiments on attention

4.0 The brain basis of attention

5.0 The brain basis of conscious experience

6.0 A summary, and some hypotheses


1.0 Introduction

Attention is often thought of as a spotlight, aiming to select some part of the world for conscious access.

The ‘spotlight’ of attention is often thought to involve frontal and parietal cortex, as well as subcortical regions



A common sense distinction between attention and consciousness:

We can ask someone to ‘please pay attention’ but not to ‘please be conscious’. In general, however, when people pay attention to something, they generally become conscious of it.

The common sense distinction between attention and consciousness suggests that there are attentional control mechanisms that often determine what will or will not become conscious …



Cortical selection and integration

Executive selective attention processes ‘select’ different sensory and cognitive processes, as if the yellow arrow can ‘point’ to any part of the diagram.

Conscious cognition is often the result of attentional selection.



Cortical selection and integration

An attentional ‘spotlight’ selects among competing inputs. Cortex can be seen as a large array of processing hierarchies for sensory, motor, and cognitive tasks.



Selective attention: voluntary and automatic

Attention can be voluntarily directed to something in our environment. This process is typically referred to as a ‘top-down’ process since the brain is voluntarily selecting the sensory information to be processed.



Another type of attention is automatic: called ‘attentional capture’, it happens when something in our environment (like a loud noise) captures our attention without our conscious attention or voluntary control.

Attentional capture is a ‘bottom-up’ process: the sensory input drives the attentional processing.



Selective attention: voluntary and automatic

In the real world, voluntary and automatic attention are generally mixed. For example, we can train ourselves to pay attention to the new ringtone we found for our cell phone.

When it rings and we suddenly pay attention to it, is that voluntary or automatic?

Visual areas involved in active and passive viewing extend to the parietal lobe



Methods for studying selective attention

Early studies of selective attention were done by Broadbent (1957) and Cherry (1953): they studied the way we can selectively listen to competing stimuli. Cherry coined the term ‘the cocktail party effect’ to describe how selective attentional processes are at work in a busy listening environment.

Selective listening: competing speech streams are sent to each ear and the subject’s task is to repeat what they hear as they hear it, called shadowing. Subjects can repeat only one stream at a time.



Methods for studying selective attention

The flanker task is an important tool for studying visual attention. The basic method is to present a fixation point (+) to the subject, and then present stimuli that ‘flank’ the fixation point, just outside the foveal region of maximum visual resolution. This task does not allow eye movements, but relies on covert shifts of visual attention.

The flanker task



Methods for studying selective attention: attentional search paradigms

Stimulus-driven attention: ‘pop-out’ vs. effortful search A well-known case of stimulus-driven attention comes from Anne Treisman’s visual search paradigm. When a target stimulus differs sharply from the surrounding stimuli, it tends to ‘pop-out’.

Task: locate the vertical red bar



Methods for studying selective attention: attentional search paradigms

Stimulus-driven attention: ‘pop-out’ vs. effortful search When the target stimulus shares features (in a conjunction search), more voluntary effort is required to locate it.

Task: locate the vertical red bar



Higher neuronal firing to an attended stimulus

A classic example of an attentional increase in sensitivity at the level of a single neuron. The flower is the preferred stimulus. This neuron (in visual cortex IT, an object recognition area) begins firing in anticipation of the preferred stimulus at a higher level than for the non-preferred stimulus.



Guiding the spotlight

If we think of attention as a spotlight, we must also ask the question what is guiding it. Brain areas like the prefrontal cortex are suggested as sources of control for voluntary attention, and the result is improved efficiency in the visual cortex.



Salience maps help guide attentional selection

What determines what object the attentional system selects?

Ultimately, attention cannot be understood without taking into account emotion, motivation, and salience.

Biologically significant stimuli draw attention: here a single cell recording shows that a monkey’s THREAT face draws more attention than a neutral face



Executive (voluntary) attention

Voluntary attention sometimes needs to go against our existing tendencies: for example, ignoring a ringing cell phone while speaking to a friend. The expected behavior is to answer the phone and executive attention processes are required to override that behavior.

The flanker task has been used to investigate brain networks that are recruited for executive attention in this type of situation. In the flanker task, the subject is

cued to expect a flanker stimulus on the left.




In this version of the flanker task, the task is to covertly (without moving the eyes) attend to the side of the screen that is cued.

In some trials, a stimulus appears on the cued side of the fixation point while on others a stimulus appears on the un-cued side.

On these trials, the subject must override the tendency to attend to the stimulus on the un-cued side and instead use executive attention to covertly attend to the cued side.

Top: the stimulus appears on the left. Bottom: the stimulus unexpectedly appears on the right.




Interestingly, the brain networks for maintaining executive attention to the cued side, overriding the tendency to attend to the side that contains a stimulus, differ from the networks that guide visual attention to an expected stimulus.

Brain regions that are involved in executive attention in the flanker task include prefrontal cortex and parietal regions.



Conscious cognition

Attention is a selective capacity, an ability to focus on one thing and not another.

Conscious cognition is closely related but not identical to attention.

We are usually conscious of the results of attentional selection, but not necessarily of selection itself.



Unconscious comparisons

How can we investigate conscious experience?

Consciousness has been used a a variable, with experiments designed to compare conscious and unconscious conditions in the same experiment using the same stimuli.

Backward masking is used to compare conscious and unconscious perception. Subjects do not perceive the smiling face, but the unconscious face still primes behavior and brain activity



Inattentional blindness

We are often unaware of visual events that occur at the very center of visual gaze. The most famous example of inattentional blindness comes from Daniel Simons’ invisible gorilla movie. When subjects are instructed to track the basketball being thrown back and forth amongst the students, they cannot ‘see’ the person in the gorilla costume walking across the scene.



Binding features into conscious objects

The concept of feature binding -- combining color, location, shape, and the like into a single neuronal assembly -- is often to be necessary for visual consciousness. Treisman suggested that an attentional spotlight was required to combine different aspects of a stimulus into a reportable event.

Treisman’s spotlight for binding visual features



Conscious events recruit widespread brain activation

There are many sources of evidence suggesting that the more we are conscious of some event, from visual perception to motor control, the more cortical activity we are likely to find.

Results of an fMRI experiment: brain activation during a sensorimotor task where subjects were asked to tap along with the sound of a metronome. Once trained on the task, the scientists varied the pace of the metronome by 3, 7, or 20%. Cortical activity increased dramatically as a function of the unpredictability of the tapping task.



Fast cortical interactions may be needed for conscious events

Recent technical advances have made it possible to record the interactivity of brain regions. Results of an experiment using visual flicker to evoke widespread brain synchrony: a flickering stimulus evokes correlated synchronous firing between active brain regions during conscious perception.



Fast cortical interactions may be needed for conscious events

It is believed that rhythmic synchrony between different brain regions may signal cooperative and competitive interactions between neuronal populations needed to perform tasks, particularly those that are conscious and under voluntary control.


6.0 A summary and some hypotheses

Selective attention to a visual stimulus seems to be guided by parts of the frontal and parietal lobes

Conscious cognition can be shown to recruit frontoparietal regions

Thus selective attention can be thought of as an act of focusing brain resources on visual cortex -- particularly the region where feature binding seems to take place.

Conscious cognition can be seen as going in the opposite direction, a visual object serving to mobilize cortical regions far beyond visual cortex alone.


6.0 A summary and some hypotheses

Selective attention can be thought of as an act of focusing brain resources on visual cortex -- particularly the region where feature binding seems to take place.

Conscious cognition can be seen as going in the opposite direction, a visual object serving to mobilize cortical regions far beyond visual cortex alone.

cognition, brain and consciousness: an introduction to cognitive neuroscience edited by bernard j....

Documents

introduction attention

spotlight of attention

brain basis of attention

automatic attention

cognitive neuroscience

conscious cognition

conscious slide

cognitive processes