Theoretical Models of Attention
Attention is defined as the ability to attend to somethings while ignoring others. There are three principle goals:
- To understand how attention enables and influences the detection, perception and encoding of stimulus events as well as the generation of actions based on the stimuli.
- To describe the computational processes and mechanisms that enable these effects.
- To uncover how these mechanisms are implemented in the brain's neuronal circuits and neural systems.
Herman von Helmholt
He did an experiment that looked at covert attention. He had participants look at a screen with letters different distances from the center. The screen was so large that the the participant could not view the screen in its entirety. Covert attention is defined as: the location to which the participant directed his/her attention could be different from the location at which he/she was looking. The participant could see the letters that were in his focus of attention better than those that were not.
E.C. Cherry
He looked at the cocktail effect, which is the idea that in a noisy environment people cal focus on a single conversation. The loudest inputs are not always the best and are not always the ones that everyone focuses on. The goal of the listener is to ignore the louder inputs, this is known as selective auditory attention. However, if the person you are talking to is boring you can attend to another conversation but still stare at the person who is talking to you. He observed the idea of dichotic listening: having two different inputs in each ear, but only attending one of those inputs. They are not able to repeat what was played in the unattended ear. However, you are able to pick up important information in an unattended ear, such as hearing your name.
Donald Broadbent
He came up with the model of selective attention, which states that there is a gating mechanism that determines what information is passed on for higher analysis. But, our mental capacity is limited so we filter our what we want and what we don't know, but some things that we don't want still get through.
Michael Posner
He came up with the spatial cuing paradigm. He carried out an experiment using cued stimuli. Participants are asked to stare at the cross in the center of the computer screen. A cue indicates where the subject should covertly attend. Then the target follows and it is either correctly or incorrectly cued. Posner found that the participants respond faster when it is correctly cued than when it is not.
Reflexive Attention
reflexive cuing: attention to an external stimuli. You will respond to the cue within 50-200 ms. He observed the phenomenon called inhibition of return, which states that you respond more slowly to target that have more space between them and the cues.
Anne Tresiman
She did an experiment that focused on the visual search paradigm. This is the idea that if something sticks out no attention is needed to find it. However, if there are more things that are alike it, it will take longer to find it; this is called conjunction search.
Attention to Features and Objects.
If cued to expect the target is moving, will we be able to discriminate the target more readily than if it is unexpectedly not moving? Marissa Carrasco looked at this idea. There was a warning tone which was followed by one of three cues: target will not move, an arrow indicating which way it will move and a double-headed arrow indicating it will move left or right. She found that at the cue is not helpful at 150 ms, at 300 ms it helps for spatial but not feature. At 500 ms it helps for both.
Neurophysiology
Raul Hernandez-Peon predicted that: the olivocochlear bundle might exert top-down control over subcortical auditory regions that project to the cortex in the service of early attentional gating of auditory inputs. He found that the activity increases in the cochlear nucleus when the animals attended to the sounds rather than when they ignored the sounds while visually attending to the mice. So, attention to something else diminishes attention to other stimulus.
Steven Hillyard looked and auditory selective attention. He asked participants to attend to sounds in the left or right ear. The auditory sensory ERPs were increased in amplitude when stimuli were attended to compared with when they were ignored. He discovered the P20-50 effect: positive polarity latency between 20-50 ms suggests an early stage of processing. He localized the M20-50 effect to the auditory cortex in the Heschel's gyri.
It is hard to compare the auditory and visual systems because the timing is very different. In the voluntary visual attention, there are changes in the visual ERPs, which begin as early as 70-90 ms after the cue. This is known as the occipital P1, when a visual stimulus appears at a location to which a subject is attending, the P1 is larger in amplitude than when the same stimulus appears at the same location but attention is focused elsewhere.
How are feature and spatial attention related? Spatial attention produces the shortest latency ERP (N2pc). Wanted to see if features were selected before spatial attention was focused on target location. They saw that 140 ms after the onset, the feature ERP was generated in the ventral occipitotemporal cortex. 30 ms after that an N2pc response was generated in more anterior regions. This study indicated that the subjects were focusing spatial attention on the target. Feature selective attention precedes visuospatial attention when the location of the target is unknown in advance.
Neuroimaging
Spatial attention leads to activation in the extra striate cortex in the hemisphere opposite to the attended side (attention on the left enhances the right side, and vice versa). Spatial attention influences the processing of visual inputs. Kastner et al saw that in the absence of focused spatial attention, when stimuli are presented simultaneously, they can interfere with one another.
Corbetta et al saw that there are changes in the extra striate cortex when people attend to stimulus features. Selective attention to color, shape etc activate distinct regions of the extra striate cortex.
Attention to objects has been studied by John Duncan. Object properties are a collection of properties that make a person/object identifiable. Duncan compared attention to location to attention to objects. He found that two perceptual judgements about the same object can be made accurately, however they cannot be made accurately about two different objects. Uncued locations that were located on the same object showed an increased activity in the V1, V2, V3 and V4, but there was no activity in these areas when the uncued location was on different ojects.
Animal Studies
Moran and Desimone: they trained animals to attended to one stimulus and ignore another. They recorded responses in the V4. There is a stronger response in the V4 when the stimulus was attended as opposed to not.
Brad Motter: activity in the V1 changes when competing stimuli were presented. Animals were trained to attend or ignore a stimuli. Motter recorded spike activity - when the animal was covertly attending, spikes were greater than when they were ignored. He also found that the amplitude of attention was alrger when competing stimlui were presented in the visual field compared to the target being alone.
McAdams and Reid: They also looked at the V1. They wanted to characterize the properties of the neurons in the V1 and then seeing if it was influenced by spatial attention. They trained monkeys to fixate on a central point and covertly attend to a black and white screen. A noise was presented to detect a small colored pixel. When the monkey saw the color pixel they were suppose to make a rapid eye movement from fixation to the location on the screen of the color. Spatial attention enhanced the responses of the simple cells but did not affect the spatial or temporal organization of their receptive fields.
Neurology and Neuropsychology of Attention
Unilateral spatial neglect is when one whole side of a person's visual world is gone. Typically the damage to the right parietal and frontal cortical areas are implicated, therefore the left visual field is gone. Some experiments have studied those with spatial neglect. They are given a line test and asked to intersect the horizontal lines on the paper right in the center of the line. They tend to bisect the line more to the right side. You not only have neglect to external stimuli, but it is in your won memory as well.
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