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Chapter 21

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Department
Neuroscience
Course
NROC64H3
Professor
Niemier
Semester
Winter

Description
Chapter 21: Attention Intro: • Attention = state of SELECTIVELY processing simultaneous sources of info; preferential processing of sensory info; selectively attend to some info & ignore rest • Interactions btn modalities may occur (performing attention-demanding VISUAL task like reading; less sensitive to incoming SOUNDS) ADHD: • Characteristics: o Inattention o Hyperactivity o impulsiveness • 5-10% of all school children worldwide • brain structures: o prefrontal cortex = smaller o basal ganglia = smaller o not sure if these differences found in children are behavioural significant; but these structures have been implicated in regulation/planning of beh • heredity, brain injury, premature birth • genes related to fxn of DA neurons: o D4 dopamine receptor gene o D2 dopamine receptor gene o Dopamine transporter gene • Common treatments: o Behavioural therapy o Ritalin (methylphenidate) = mild CNS stimulant (amphets)  Inhibits DA transporter = increases post-syn effect of DA  Decreases impulsiveness & inattention  Long-term use? Behavioral Consequences of Attention Shifting attention to some location on retina enhances visual processing by: enhanced detection and faster reaction times. Enhanced Detection • Experiment: o Direct visual attention to diff location o Fixate on central point; say whether stimulus flashed on right, left of fixation point or not at all o Trial begins w/ cue at fixation point  cue = + (neutral),  or  o Cue extinguished, variable delay period during which fixation point o ½ trails = no further stimulus; other ½ of trials = small target circle on R or left for 15 ms o initial cue at fixation point used to direct attention  if target appeared to the cued side, the cue was valid  if target appeared opposite to cued side, the cue was invalid o results:  when central cue is +, detected target stimulus 60% of the trials in which one was presented  when central cue is , detected target stimulus on R 80% of trials in which one was presented; but when central cue is , detected target stimulus on L 50% of trials in which one was presented there o expectation of observer based on central cues influenced her ability to detect subsequent targets  arrow cues caused observer to shift attention to side where arrow pointed, EVEN THO EYES DIDN’T MOVE  covert shift of attention = easier to detect flashed targets compared to trials where central cue was +  observer less sensitive to targets on opposite side of where cue pointed • Conclusion: attention makes things easier to detect Faster Reaction Times • Experiment similar as above: attention increases speed of rxn in perceptual studies o Preceding target stimulus was cue stimulus (same as b4); in this experiment, observer has to wait til he perceived a stimulus on either R or L and then had to push a button ; +,  or  were cue stimulus which indicated if neutral cue, or target stimulus would appear on the side of the central stimulus cue arrow o If central cue was +, 250-300 ms to press button o If central cue was arrow that correctly indicated where target would appear, rxn time = 20-30 ms faster o If central cue was arrow that incorrectly indicated where target would appear, rxn time = 20-30 ms slower • Rxn time includes: o Time for transduction in visual system o Time for visual processing o Time to make decsion o Time to code for finger mvt o Time to press button • But still saw reliable effect depending on which way arrow was point – directed the person’s attention • Possible that attention can alter speed of visual processing or time taken to make decision about pressing buttonNeglect Syndrome as an Attentional Disorder • Ignore things on one side of centre of gaze = perhaps a unilateral deficit in attention • Most common = damage to right cerebral hemi, therefore neglect left side of life • Denial • Distorted sense of space • Posterior parietal cortex of right hemi; other areas: o Prefrontal cortex of right hemi o Cingulated cortex o others • posterior parietal cortex = involved in attending to objects at diff positions in extrapersonal space = neglect may be disruption in ability to shift attention; evidence for this hypothesis = objects in right visual field of patients are sometimes abnormally effective capturing attention and patients may experience difficulty disengaging their attention from an object on this side • right hemi = more dominant for understanding spatial relationships and solving complex puzzles; Physiological effects of Attentions FMRI of Attention to Location • BEHAVIORAL studies show that enhancements in detection and rxn time are selective for spatial location o When we know where an impt stimulus is more likely to appear, we move our attention to it and process the sensory info w/ greater sensitivity/speed • Selective changes in brain activity associated w/ spatial shifts in attention o Study 1:  Subjects in fMRI viewed stimulus = colored line segments arranged in circular sectors at several distances from central fixation point  Subject instructed which sector to pay attention to, located changed every 10 sec  During 10 sec, color and orientation of line segments changed every 2 sec  Press one button if lines were blue&horizontal or orange&vertical; nd press a 2 button if lines were blue&vertical or orange&horizontal  This task forces subject to attend to particular sector of stimulus while keeping gaze fixed at centre  Results: • Brain activity recorded with the attended sector at 4 locations at increasing distance from fixation point • Areas of highest brain activity move away from the occipital pole as the attended sector moves out from fovea • Pattern of brain activity shifts retinotopically, even tho visual stimuli are same regardless of which sector is attended • Images show the neural effect of the spotlight of attention moving to diff locations • This is consistent w/ the behavioural observation that visual attention can be moved independently of eye postion PET imaging of Attention to Features • We don’t just pay attention to location; also pay attention to features which will enhance performance • This attention to features is reflected in brain activity = PET o Study 1:  Same-different discrimination task  Image flashed on screen for 0.5 sec; delay period; another image flashed; each image = made of small elements that could vary in shape, color, speed of motion  2 images same or diff?  all characteristics could change between the 2 images, but the observer was instructed to base his same-diff judgments on ANY ONE or ALL of the attributes  but in this experiment, the brain activity would simply indicate where neurons were activated by the visual patterns;  added following dimensions to the experiment: o Study 1a:  Selective attention experiments:  Subjects view stimuli and performed the same-diff task after being told to pay attention to just one of the features o Study 1b:  Divided attention experiments:  Subjects simultaneously monitored all features and based their same-diff judgments on changes in any feature o Then, subtracted the divided-attention responses from selective-attention responses to obtain an image of changes in brain activity associated WITH ATTENTION TO ONE FEATURE o Results:  Diff areas of cortex = higher activity when diff attributes of stimuli discriminated  V
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