multiplechoicequestions.docx

Attention --------- \ OUTLINE **273** \ TAKE-HOME MESSAGES - Attention is the ability to focus awareness on one stimu- lus, thought, or action while ignoring other irrelevant stimuli, thoughts, and actions. - Arousal is a global physiological and psychological brain state, where...

Attention --------- \ OUTLINE **273** \ TAKE-HOME MESSAGES - Attention is the ability to focus awareness on one stimu- lus, thought, or action while ignoring other irrelevant stimuli, thoughts, and actions. - Arousal is a global physiological and psychological brain state, whereas selective attention describes what we attend and ignore within any specific level (high vs. low) of arousal. - Attention influences how we process sensory inputs, store that information in memory, process it semanti- cally, and act on it. ### The Anatomy of Attention ### The Neuropsychology of Attention ##### Neglect ##### Neuropsychological Tests of Neglect 0 --50 50 0 --50 --100 --50 0 50 100 Horizontal position ( ˚ ) ##### Extinction ##### Comparing Neglect and Bálint's Syndrome - How does attention influence perception? - Where in the perceptual system does attention influence perception? - How is attention allocated in space versus to stimu- lus features and objects? - What neural mechanisms control attention? TAKE-HOME MESSAGES - Unilateral spatial neglect may result from damage to the right parietal, temporal, and/or frontal cortices, as well as subcortical structures. This kind of damage leads to reduced attention to and processing of the left-hand side of scenes and objects. - Neglect is not the result of sensory deficits, because visual field testing shows that these patients have intact vision. Under the right circumstances, they can easily see objects that are sometimes neglected. - A prominent feature of neglect is extinction, the failure to perceive or act on stimuli contralateral to the lesion (contralesional stimuli) when presented simultaneously with a stimulus ipsilateral to the lesion (ipsilesional stimulus). - Neglect affects external personal hemispace and objects as well as internal memory for objects arrayed in space. ### Models of Attention ##### Hermann von Helmholtz and Covert Attention a. Hermann von Helmholtz (1821--1894). b. Experimental setup by Helmholtz to study visual attention. Helmholtz observed that, while keeping his eyes fixated in the center of the screen during ##### The Cocktail Party Effect ##### Early Versus Late Selection Models ##### Quantifying the Role of Attention in Perception TAKE-HOME MESSAGES - Attention involves both top-down (voluntary), goal-direct- ed processes and bottom-up (reflexive), stimulus-driven mechanisms. - Attention can be either overt or covert. - According to early-selection models, a stimulus need not be completely perceptually analyzed before it can be selected for further processing or rejected as irrelevant. Broadbent proposed such a model of attention. - Late-selection models hypothesize that attended and ignored inputs are processed equivalently by the per- ceptual system, reaching a stage of semantic (meaning) encoding and analysis where selection may occur. - Our perceptual system contains stages at which it can process only a certain amount of information at any given time, what are called limited-capacity stages which result in *processing bottlenecks*. Attention limits the information to only the most relevant, thereby preventing overload of the limited-capacity stages. - Cuing tasks, where the focus of attention is manipulated by the information in the cue, are often used to study the effect of attention on information processing. - Spatial attention is often thought of metaphorically as a "spotlight" of attention that can move around as the person consciously desires, or that can be reflexively attracted by salient sensory events. ### Neural Mechanisms of Attention and Perceptual Selection ##### Voluntary Spatial Attention 0 100   Saccade 0 0 --20 0 Time (ms) Robert Desimone and John Duncan (1995) pro- posed a *biased competition model* for selective attention.  -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Visual areas Time (s) Time (s) a. Coronal MRI section in one participant, where the pure sensory responses in multiple visual areas are mapped with meridian mapping (similar to that used in Figure 7.20). **(b)** The percentage of signal changes over time in areas V1 and V4 as a function of whether the stimuli were presented in the sequential (SEQ) or simultaneous (SIM) condition, and as a function of whether they were unattended **(left)** or whether attention was directed to the target stimulus (**right**, shaded blue). In V4 especially, the amplitudes during the SEQ and SIM conditions were more similar when attention was directed to the target stimulus (shaded blue areas at right) than when it was not (unshaded areas). b. Viewed from greater distance, multiple flowers are present within the smaller V4 receptive field and the larger IT receptive field. 1.6˚ 4.6˚ ##### Reflexive Spatial Attention 6 a. **b c** 0 0 15 2 1 --8 2.3 8 0 a. Before stimulus onset, an arrow cue at fixation instructed the participants which hemifield to attend. Next, a checkerboard stimuli presented bilaterally for 18 s (shown as blue shaded area in **c**). The task was to detect randomly occurring luminance changes in the flickering checks in the cued hemifield. b. Functional MRI activations (increased BOLD responses) were observed in the LGN (red box) and in multiple visual cortical areas (green box). **(c)** Increased activations were seen when the stimulus in the hemifield contralateral to the brain region being measured was attended. The effect was observed both in the LGN **(top)** and in multiple visual cortical areas **(bottom)**. 250 200 150 100 50 500 400 300 200 100 0 0 100 200 b. Time from stimulus onset (ms) ##### Visual Search Locus of cued attention Phosphene 300 1.5 1.2 0.9 0.6 0.3 0.0 1.5 1.2 0.9 0.6 0.3 0.0 Cued Uncued 2 4 6 **O** ##### Feature Attention 0.8 0.6 0.4 0.2 0 --0.2 **b** Calibration 2 μV \+ a. ERPs recorded to right visual field stimuli when subjects covertly attended right (solid line) and when subjects attended left (dotted line) independently of stimulus color or which color was attended. b. ERPs to right visual field stimuli when attending right and the color of the evoking stimulus was attended (solid line) versus when attending right but the unattended color was presented there (dotted line). **(c)** Difference ERPs associated with attended versus unattended spatial locations. **(d)** Difference ERPs associated with stimuli of attended versus unattended color at the attended location (solid line) and the unattended location (dotted line). The arrows in the right panels indicate the onset of the atten- tion effects, which was later in this experiment for color attention. Positive voltage is plotted downward. dLO MOG 300 ms 300 ms b. Motion attention c. Color attention a. Blocks began with a letter cue (*M* or *C*) indicating that participants should attend to either motion (fast versus slow) or color (red versus orange), respectively, and press a button representing the indicated feature. Dots would appear, and they randomly would either move or change color. In this way, d. responses to changes in motion (or color) could be con- c. When color was attended, ventral area V4 (V4v in the posterior fusiform gyrus) was modulated. This relation was found for fMRI BOLD responses (shown as the reddish yellow blobs on the MRI) and for MEG measures taken in a separate session (shown as circles with arrows in **(b)** and **(c)**, overlap- ping regions of significant BOLD signal change). The high temporal resolution of the MEG measures indicated that the latency of the attention effect after the onset of the moving or color arrays was about 100 ms. **(d)** Retinotopic mapping on a single participant verifies the extrastriate region associ- ated with the motion and color attention effects on flattened cortical representations. ##### Interplay Between Spatial and Feature Attention  When the attended array contained both the attended (red) and unattended (green) dots at the same time--- Target Distracter ##### Object Attention 800 750 700 Valid trial 0.1 0 Cued ##### Review of Attention and Perceptual Selection Mechanisms Attend V1a Right hemifield Fixation Visual areas and attention b 0.1 0.08 0.06 0.04 0.02 0 Neuronal coherence 0.1 0.08 0.06 0.04 0.02 0 TAKE-HOME MESSAGES - Spatial attention influences the processing of visual inputs: Attended stimuli produce greater neural responses than do ignored stimuli, and this process takes place in multiple visual cortical areas. - Highly focused spatial attention can also modulate activ- ity in the visual system in the subcortical relay nuclei in the thalamus, thereby providing strong evidence for early- selection models of attention. - Reflexive attention is automatic and is activated by stimuli that are conspicuous in some way. Reflexive at- tention also results in changes in early sensory process- ing, although only transiently. - A hallmark of reflexive attention is inhibition of return--- the phenomenon in which the recently reflexively at- tended location becomes inhibited over time such that responses to stimuli occurring there are slowed. - Extrastriate cortical regions specialized for the perceptual processing of color, form, or motion can be modulated dur- ing visual attention to the individual stimulus features. - Selective attention can be directed at spatial locations, at object features, or at an entire object. ### Attentional Control Networks 0.6 0.5 0.4 0.3 FFA Spatial Motion selection Form selection, object selection ##### Dorsal Attention Network: Frontoparietal Attention System Attend R \> Attend L  --0.1 Attend a. Coronal sections through a template brain, showing the activations in posterior brain regions (in red) coding motion (MT+; **top row at crosshairs**) and faces (FFA; **bottom row at crosshairs**) that were induced by TMS to FEF when participants were attending motion **(left)** and attending faces **(right)**. The maximum activations, are seen in MT+ when attending motion **(top left)** and in the FFA when attending faces **(bottom right)**. **(b)** Graph of the differential activity evoked in MT+ (green) and FFA (red) when attending motion **(left)** and faces **(right)**. a. Passive fixation (no attention) b. Saccade to stimulus (monkey attends to stimulus) a. The monkey passively fixates while a lateral-field stimulus is presented, generating some action potentials from the neuron **(right)**. b. When the monkey has the task of making a saccadic eye movement to the target when it appears the neurons showed increased firing to the stimulus. c. When the animal must keep its eyes fixated straight ahead, but is required to reach to the target, the neuron increases its firing rate to targets that are presented and covertly attended. Thus, the neuron is spatially selective---a sign of covert attention. Light Light ##### Ventral Right Attention Network a. Behavioral performance from one monkey is plotted. Smaller values on the y-axis indicate better performance because this means the monkey could detect the probe orientation at a lower stimulus contrast. (*red curve*) Probe appeared at the unattended location where the distracter had appeared. (*blue curve*) Probe appeared at the attended location, i.e., the saccade target. **(b)** Neuronal responses from the same monkey are plotted. See the text for details. ##### Subcortical Components of Attention Control Networks b 450 400 400 350 300 1,000 800 600 400 ##### Review of Attentional Control Networks \ TAKE-HOME MESSAGES - Current models suggest that two separate frontoparietal cortical systems direct different attentional operations during sensory orienting: *a dorsal attention network*, con- cerned primarily with orienting attention, and *a ventral attention network*, concerned with the nonspatial aspects of attention and alerting. The two systems interact and cooperate to produce normal behavior. - The dorsal frontoparietal attention network is bilateral and includes the superior frontal cortex, inferior parietal cortex (located in the posterior parietal lobe), superior temporal cortex, and portions of the posterior cingulate cortex and insula. - The ventral network is strongly lateralized to the right hemisphere and includes the posterior parietal cortex of the temporoparietal junction (TPJ) and the ventral frontal cortex (VFC) made up of the inferior and middle frontal gyri. In addition, there are subcortical networks that include the superior colliculi and the pulvinar of the thalamus