W6.1 NEURONAL mechanisms of attention Flashcards
(11 cards)
How did Chelazzi et al (1993) show neuronal attention for specific preferences for particular stimuli in monkeys?
Chelazzi et al trained monkeys to make an eye movement towards a target- they were cued which stimuli to respond to, so, if they saw a rectangle cue, they had to make an eye movement towards the rectangle and ignore the triangle
They found (top left graph) that individual neuron’s response initially responded equally strongly regardless of whether the preferred stimulus is the target- neuron’s firing remains high. If the nonpreferred stimulus was the target, response of the neuron is suppressed
Shows that the neuronal responses in the inferior temporal cortex are competitive- if the neuron’s preferred item is the target then the response remains high and the item wins the competition for attention, however if the non preferred item is the target then neuronal firing drops off
Suggests that the attentional template is formed by modulation of brain regions that process the relevant object
see figure 16
What three things does Chelazzi’s findings tell us about attention?
- Attentional competition occurs at the level of individual neurons- a key function may be to prepare for response and suppression in relevant neurons- involves both excitation (incr firing rate of neurons that prefer a stimulus) and inhbition (suppression of firing rate for neurons that do not show such a preference)
- Modulation of neuronal responses by attention occurs well before response occurs
- Competition occurs not in a separate attentional brain region but in the regions that process the visual features of relevant and irrelevant objects- the same neurons that process the visual features of an object are co-opted by the attention system to resolve the competition for selection
What evidence is there from fMRI studies to suggests that attention effects on the primary visual cortex (V1) activation?
Researchers presented visual stimuli in different segments of a circle individually and used retinotopic mapping to examine which areas of visual cortex were sensitive to visual stimulation in different regions of space- they then taught ppts to associate certain numbers w different segments and presented these by saying them (auditory)- ppts had to perform a certain task to judge the colour and orientation of lines in a specific segment of the array
Patterns of activation in V1 were exactly the same for visual stimulation and attention- effects occurring in V1 demonstrate that attention enhances processing in the earliest stages of visual processing during attentional cueing
What fMRI evidence is there for attentional modulation of neuronal signals in V4? (Kastner et al)
Coloured patterns presented either sequentially or simultaneously to subjects in the MRI scanner
The overall level of visual stimulation was exactly the same, but all items presented simultaneoulsy could suppress action in the V4- activation higher in the sequential condition
Ppts were then asked to attend to one of the colour patches in both conditions and found that this different disappeared, as when attention is directed to a superficial stimulus, it gets rid of this modulation effect
What fMRI evidence is there for attentional modulation of neuronal signals in the FFA and PPA? (O’Craven et al 1999)
Researchers presented semi transparent images with a picture of a face and a house overlaying each other, one jittering and one static- they asked ppts to attend to either moving or static objects
If the face was moving, there was higher activation in the FFA- if the house was moving, then it was much lower
If attention was directed towards the static object, attention was more directed to the PPA- whatever the ppt was attending to was modulated by activity in the FFA or PPA
What do neuroimaging studies show in relation to attentional modulation?
Show attentional modulation of neuronal signalling throughout the visual cortex, both early in the processing stream e.g. in the V1 and late in the processing stream e.g. in category specific object recognition areas e.g. FFA. Evidence points to an attentional system that can operate flexibly at different stages depending on task demands
What did Lavie et al find in their perceptual load theory study and how can this be explained?
They found the result to be counterintuitive- low perceptual load made their reaction time slower. Explanation for this was: in the high perceptual load condition, perceptual capacity is used by the task of trying to find the target and there is none left for the distractor, acting as support for early selection- intense focus on the task at hand means you have no energy to look at other things
In the low perceptual load condition, the main task does not use up all perceptual capacity so there is some left to process the distractors- this acts as support for late selection
Where does attentional modulation of neuronal signalling in sensory specific brain regions occur and what does this suggest?
Throughout the sensory pathways, suggesting attention is a flexible system for resolving competition for awareness at multiple different levels
What evidence is there that the attentional modulation of visual cortical signals depend on perceptual load?
Schwartz et al (2005)- researchers presented ppts with displays for which they had to complete a task at the centre. Checkerboard in scanner- lots of activation in primary vC- task either low load or high load
Neuronal parallel of behavioural results- greater activation in visual cortex from low load condition and high load condition. Ppts unaware of peripheral things going on around them- shows how attention can operate early or late in visual processing depending on what you are doing
What evidence is there for top down bias signals originating in frontal cortex effects of TMS over frontal eye fields on activation in the visual cortex?
Taylor et al 2006- TMS causes a disruption of normal response in posterior brain regions- clear evidence that there seems to be a different source of these attentional signals but some signal sent from frontal cortex to posterior sensory specific brain regions
Findings suggest that attentional selection may involve long distance interactions between prefrontal and visual cortex
Hypothesised that during attentional tasks, the prefrontal cortex sends biasing signals to sensory specific regions of the cortex, enhancing activation in task relevant regions and suppressing activation in task irrelevant regions
What do the five frequency bands of EEG tell us?
Neuronal signals oscillate at particular frequencies
Different frequencies might correspond to different functions
Frequency synchronisation between brain regions might support selective attention
