Attention 2024.pptx

CHAPTER 7 Attention Cognitive Neuroscience, 5th edition © 2019 by W. W. Norton & Company Big Questions 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 atte...

CHAPTER 7 Attention Cognitive Neuroscience, 5th edition © 2019 by W. W. Norton & Company Big Questions 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? 2 Topics covered Why is attention necessary? The cocktail party effect. Difference between early and late selection theories. The difference between endogenous and exogenous attention. The difference between spatial, feature and object attention. Experimental evidence for these different types of attention. Attentional networks Attentional deficits Why is attention necessary? Attention is necessary for conscious perception Attention Definition: Attention is the process by which the mind chooses from among the various stimuli that strike the senses at any given moment. 5 Divided Attention Cocktail Party Effect 6 Early Versus Late Selection Models Early Late 7 Dichotic Listening 8  Evidence for early selection Event-related potentials in a dichotic listening task. The solid line represents the average voltage response to an attended input over time; the dashed line, the response to an unattended input  Evidence for early selection Early auditory cortical responses are affected by attention.  Different types of attention Exogenous attention (transient, bottom-up, automatic) Endogenous attention (sustained, top-down, voluntary) Quantifying Spatial Attention (1) How does manipulating the cue impact performance? 12 ERP and Reflexive Cuing Exogenous 13  What is the difference between spatial, feature based, and object based attention? 1. Spatial attention: attention to a specific location in space, irrespective of what is present at that location. 2. Feature based attention: attention to specific stimulus features irrespective of where they are in our environment. 3. Object based attention: attention to an entire object Single cell electrophysiology and visual attention Cartoon of a typical paradigm used in single cell electrophysiology studies Single neuron firing with spatial attention in area V1 and V2 of macaque monkeys  Previous slide Single neuron firing rates in V1 and V2 with spatial attention. The stimuli and task were as follows: (a) A fixation point appeared in the middle of the screen. (b) Small marker stimuli appeared at all potential target locations. (c) The animal was cued to covertly attend to the one location indicated by the marker that remained when the others were extinguished. In the left-hand column the cue indicates that attention should be directed to the lower left location, which was also the location of the receptive field of the neuron (indicated by the dashed circle only). In the right column, the cue directs attention to the upper right location, away from the neuron’s receptive field. (d) The target array consisting of oriented bars appeared, one bar being in the attended location and the others being at locations that were ignored. (e) Raster plots showing the responses (spikes) of two representative neurons from visual areas V1 (top) and V2 (bottom). The stimulus array (see part (d)) appears at time = 0 ms (upright bars). For each neuron (e.g., Neuron 1) in each visual area (e.g., area V1), the raster shows the firing rates by indicating each spike as a small tick mark. Each row of tick marks indicates an individual trial; for example, for Neuron 1 in V1 eight trials are shown, and for Neuron 2 in V1 six trials are shown. A glance reveals that, for each neuron in both V1 and V2, there are more spikes per unit time (the rasters have more ticks and appear more dense) when the neuron’s receptive field was covertly attended than when ignored. Feature and object based attention How are features represented in the brain? How are objects represented in the brain? fMRI evidence for feature selective attention in different human brain areas. For figure legend see next slide Previous slide: Attention modulates activity in feature-specific visual cortex. (a) Stimuli and task parameters. Each block of several stimuli began with a letter cue (M or C) indicating that the subjects 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 would either randomly move or change color. In this way, responses to changes in motion (or color) could be contrasted when motion was attended versus when color was attended. (b) When motion was attended, activity in lateral occipitotemporal regions (human MT/V5) was modulated. (c) When color was attended, ventral area V4 (V4v in the posterior fusiform gyrus) was modulated. This relation was found both 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), overlapping regions of significant BOLD signal change). The high temporal resolution afforded by 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 subject verifies the extrastriate region associated with the motion and color attention effects. Object Attention 22  Object based attention Effects of objects on spatial attention. (a) Stimulus display used to demonstrate behavioral spatial and object attention effects. Wrenchlike objects were continually presented on the screen and were oriented horizontally (left and middle) or vertically (right). On each trial, a centrally located cue (shown here as a white arrow for ease of presentation) indicated the most likely location of subsequent targets that required a fast response whether at the cued location (frequent) or elsewhere (infrequent). (b) Reaction times to targets were fastest when the cues validly predicted the target location, were slowest to invalid cue trials when the target appeared on a different object, and were intermediate in speed for invalid trials where the target appeared on the same object. (c) Stimulus display for the fMRI experiment where the upper left location was always cued and where the target appeared on most trials. Uncued locations in the upper right quadrant (for example) could be either on the same object as the cued location (middle) or on a different object (right). The black arrows above each panel indicate the visual field locations that corresponded to regions of interest in the visual cortex from which hemodynamic responses were extracted. (d) Hemodynamic responses (percentage signal change) are shown as bar graphs from regions of interest in visual cortical areas V1 to V4. In each area, the largest response is in the cued location, and smaller responses are obtained from uncued locations (the main effect of spatial attention). Importantly, when the uncued location was on the same object as the cued location, the fMRI activation was larger, demonstrating the effect of object attention. (e) Flattened left visual cortex (pole at bottom) from MRI showing retinotopic mapping of V1 to V4, and the hemodynamic responses (right) extracted from the activated regions corresponding to the uncued visual field location when that location was in the same (red curve) and different (blue curve) objects as the cued location (which was located in the opposite hemisphere, not shown). Feature based attention describes: a) A specific form of spatial attention. b) The fact that specific stimulus features (e.g. motion, color, shape) are represented in distinct areas of the brain (motion in MT, color in V4). c) The ability to attend to specific features, across the visual space. d) the activation of attention command centers by specific features. e) B and c are correct. Object based attention describes: f) Our ability to attend to objects in space. g) The fact that attention to subparts of an object, ensures that other parts of that object are automatically better processed as well. h) That attention should be given to objects in our motion path. i) That object representing areas of the brain show attentional modulation. j) None of the above. 1. What is the attentional network? 2. How does the attentional network influence sensory processing? 3. Do different forms of attention engage different networks? 4. Midbrain attentional networks and cortical attentional networks. 5. Premotor theory of attention 6. Neurology – attention can be affected by many types of brain lesions 3 25  What is the attentional network? Spatial cuing paradigm + + + fixation cue delay stimulus time 8s 500 ms 5 26  What is the attentional network? Measured by: Event-related fMRI Long delay between cue (directing attention) and stimulus allows to identify which areas are part of the attentional control network. Why? - Response after cue offset Þ Delineates the attentional control network -Response related to stimulus onset => Delineates areas activated by stimulus and task 6 27  What is the attentional network? 7 28 spatial cue and Attentional control network activated in response to an attention-directing identified using event-related fMRI in a cuing paradigm.  What is the attentional network? The event related fMRI experiment revealed an ensemble of areas that were selectively active when the cue was presented, i.e. these areas (blue) are involved in attentional control. The areas highlighted in red/yellow of the previous slide became only active when the stimulus was presented, i.e. they are involved in stimulus processing, but not in directing attention (even if their activity can be modulated by attention). 8 29  Lesions and different control networks 26 Lateral view of the right hemisphere, showing the major anatomical regions implicated in neglect, including the temporoparietal junction (TPJ), angular gyrus,30supramarginal gyrus, and superior temporal gyrus.  Lesions and different control networks Different forms of neglect correlate with dysfunction in different 31 brain regions. 29 Key points to know: Two main types of voluntary eye movements Early vs. late selection theories Endogenous vs exogenous attention What is the evidence for attentional modulation of single cell responses? What does the biased competition theory of attention state? Why would you expect feature selective attention signals in different areas of the brain? (Hint how are different features represented in the brain?) What is the evidence of object based attention (task, behaviour, imaging results?) Attention (selection) networks. Attentional deficits