Chapter 7 - Attention.docx

##### No man is lonely eating spaghetti, for it requires so much attention. *Christopher Morley* CHAPTER Attention ========= - Does attention affect perception? - To what extent does our conscious visual experience capture what we perceive? - What neural mechanisms are involved in th...

##### No man is lonely eating spaghetti, for it requires so much attention. *Christopher Morley* CHAPTER Attention ========= - Does attention affect perception? - To what extent does our conscious visual experience capture what we perceive? - What neural mechanisms are involved in the control of attention? **275** ### Selective Attention and the Anatomy of Attention 1. TAKE-HOME MESSAGES - Selective attention is the ability to focus awareness on one stimulus, thought, or action while ignoring other, ir- relevant 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 versus low) of arousal. - Specific networks for the control of attention include cortical and subcortical structures. - Attention influences how we process sensory inputs, store that information in memory, process it semanti- cally, and act on it. 2. ### The Neuropsychology of Attention Neglect −50 50 0 −50  Comparing Neglect and Bálint's Syndrome - *Simultanagnosia* is a difficulty in perceiving the visual field as a whole scene, such as when the patient - *Ocular apraxia* is a deficit in making eye movements (saccades) to scan the visual field, resulting in the inability to guide eye movements voluntarily: When the physician overlapped the spoon and comb in space as in Figure 7.1c, the Bálint's patient should have been able, given his direction of gaze, to see both objects, but he could not. - How does attention influence perception? - Where in the perceptual system does attention influ- ence perception? - What neural mechanisms control what we attend? - *Optic ataxia* is a problem in making visually guided hand movements: If the doctor had asked the \ TAKE-HOME MESSAGES - Unilateral spatial neglect may result from damage to the right parietal, temporal, or frontal cortices, as well as to subcortical structures. This kind of damage leads to reduced attention to and processing of the left-hand - Neglect is not the result of sensory deficits, because visual field testing shows that these patients have - 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). - Patients with Bálint's syndrome have three main deficits characteristic of the disorder: difficulty perceiving the visual field as a whole scene, an inability to guide eye movements voluntarily, and difficulty reaching to grab an object. ### Models of Attention \ Hermann von Helmholtz and Covert Attention The Cocktail Party Effect Early-Selection Models Versus Late-Selection Models a. Valid trial b. Invalid trial c. Neutral trial Quantifying the Role of Attention in Perception 300 250 200 TAKE-HOME MESSAGES - Attention involves both top-down (voluntary), goal- directed processes and bottom-up (reflexive), stimulus- driven mechanisms, and it 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, and that selection can occur only upon reaching a stage of semantic (meaning) encoding and analysis. - Our perceptual system contains limited-capacity stages at which it can process only a certain amount of informa- tion at any given time, resulting in processing bottle- necks. Attention limits the information to only the most relevant, thereby preventing overload. - Spatial attention is often thought of metaphorically as a "spotlight" of attention that can move around as the per- son consciously desires or can be reflexively attracted by salient sensory events. 4. ### Neural Mechanisms of Attention and Perceptual Selection Voluntary Visuospatial Attention − P2 300 ms \+ Primary 10 5 0 --5 --10 0 --20 0 Time (ms)  Q 0.7° 6 0 250 200 150 100 50 0 500 400 300 200 100 0 light flash---*but only for a short time after the flash*, about 200 50--200 ms. These effects tend to be spatially specific; Reflexive Visuospatial Attention Visual Search **c** 700 ms 400--250 ms a. Stimuli were shown to participants, who were told to search for either a blue or a green *t* on each trial, and to indicate by pushing a button whether that item was upright or inverted. The red *t*'s were always irrelevant distractors. An irrelevant white, outlined square was flashed (for 50 ms) as a probe stimulus around either the blue or the green *t*. Moreover, the white probe could be flashed around the blue or green item when the colored item was the target, or when it was merely an irrelevant distrac- tor. In this way, the amplitude of the probe ERP could be taken as an index of the location and strength of spatial attention just after the onset of the search array, at the point where participants would have located the target and discriminated its form (upright or inverted). The white probe was flashed either 250 ms or 400 ms after the onset search array. The search array remained on the screen for 700 ms. b. The irrelevant white probe elicited a larger sensory-evoked occipital P1 wave when it occurred at the location of a relevant target (e.g., blue *t*) compared to the irrelevant target (e.g., green *t*). These findings support the idea that focal spatial attention is directed to the location of the target in the array during visual search. The corresponding amplitude modulations of sensory-evoked activity in early visual cortex that occur with the focused attention mirror those seen in spatial cuing paradigms. Feature Attention Interstimulus 0.8 0.6 0.4 0.2 0 --0.2 a. Each trial began with a warning tone that was followed by one of three types of cues. The cues indicated either the location or the direction of motion of the subsequent target if present, and the double-headed arrow indicated an equal probability that the location or direction of motion would be left or right. **(b)** The dif- ference in accuracy of detection (valid versus neutral cue) of the moving dots is plotted here as a function of cue-to-target stimulus onset asynchrony (SOA), for both the spatial attention and feature attention conditions. (SOA is the amount of time between the start of one stimulus and the start of another stimulus.) Note that in both cases, the selective-attention effects build up over time, such ERPs to: a. **c** Attended-minus-unattended difference ERPs N2 b. **d** dlOC MOG c. Attend color Object Attention 650 0 **c d** 0.1 0 a. **b** Experiment 1 **c** Experiment 2 2.5 2 1.5 1 0.5 0 0.60 0.55 0.50 0.45 0.40 0.35 0 **Attend V1a** Right hemifield Fixation  b. Visual areas and attention 0.1 0.08 0.06 0.04 0.02 0 0.1 0.08 0.06 0.04 0.02 0 c. V4--V1a coherence **d** V4--V1b coherence a. Grating stimuli were presented that were in the same V4 receptive field (larger box with dashed, green outline) but were in different receptive fields in area V1 (small boxes outlined in red or blue). b. Diagram of the left visual cortex of the macaque monkey, showing two regions in V1 (V1a and V1b) that mapped the stimuli shown in (a), as well as how these stimuli were represented in higher- order visual area V4. The arrows indicate hypothesized coherences in attention. **(c, d)** Neuronal coher- ence is shown between regions of V1 and V4, depending on which stimulus is attended (see text for more details). TAKE-HOME MESSAGES - Spatial attention influences the processing of visual in- puts: Attended stimuli produce greater neural responses than do ignored stimuli, and this process takes place in multiple visual cortical areas. - 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 attended lo- cation becomes inhibited over time such that responses to stimuli occurring there are slowed. - Extrastriate cortical regions specialized for the perceptual processing of color, shape, or motion can be modulated during visual attention to the individual stimulus features. - Selective attention can be directed at spatial locations, at object features, or at an entire object. - Attention increases coherence of neuronal oscillations between visual areas. 5. ### Attentional Control Networks The Dorsal Attention Network Attend left Attend right 4 2 0 4 3 2 1 b. Cues V4 recording 0.2 0.1 0.0 −0.1 a. Coronal sections through a template brain, showing acti- vations in the posterior brain regions (in red) coding motion (MT1; 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 MT1 when attending motion (top left) and in the FFA when attending faces (bottom right). b. Graph of the differential activ- ity evoked in MT1 and FFA when Light a. Passive fixation (no attention) b. Saccade to stimulus (monkey attends to stimulus) c. Reach 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 show increased firing to the stimulus. **(c)** When the animal must keep its eyes fixated straight ahead but is required to reach toward 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. LIP 1.2 1.0 0.8 1.2 1.0 0.8 0.6 0 400 800 The Ventral Attention Network **c** Subcortical Components of Attentional Control Networks a. This diagram of the entire left thalamus shows the divisions of the major groups of nuclei, and the relationships between the visual lateral geniculate nucleus (LGN) and the pulvinar, and between the auditory medial geniculate nucleus (MGN) and the pulvinar. **(b)** These cross sections through the pulvinar show at a. Ipsilesional attention b. Contralesional attention 300 450 400 350 300 450 400 350 c. Reorientation after invalid cue 300 1,000 800 600 400 0 0.2 0.2 0.15 0.15 0.05 a. VLP--TEO **b** V4--TEO TAKE-HOME MESSAGES - Current evidence suggests that two separate fronto- parietal cortical systems direct different attentional control operations during orienting: a *dorsal attention network*, concerned primarily with orienting attention, and a *ventral attention network*, concerned with the nonspa- tial 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. #### Summary #### Key Terms #### Think About It 1. Do we perceive everything that strikes the retina? What might be the fate of stimuli that we do not perceive but that nonetheless stimulate our sensory receptors? 2. Are the same brain mechanisms involved when we focus our intention voluntarily as when our attention is captured by a sensory event, such as a flash of light? 3. Is neglect following brain damage a deficit in percep- tion, attention, or awareness? 4. Compare and contrast the way attention is reflected in the activity of single neurons in visual cortex versus parietal cortex. Can these differences be mapped onto the distinction between attentional control and atten- tional selection? 5. What brain networks support top-down control over the focus of attention, and how might these top-down influences change the way that interconnected regions of sensory cortex process information with attention? #### Suggested Reading  **323**