Chapter 6: Visual Attention

1. Chapter 6: Visual Attention

2. Overview of Questions Why do we pay attention to some parts of a scene but not to others? Do we have to pay attention to something to perceive it? Does paying attention to an object make the object �stand out�?

3. Attention and Perceiving the Environment Divided attention - paying attention to more than one thing at one time This ability is limited, which has an impact on how much we can process at once Driving home from Birmingham Selective attention - focusing on specific objects and filtering out others

4. Why is Selective Attention Necessary? Some aspects of the environment are more important and interesting than others The visual system has evolved to operate in this fashion There is too much incoming stimulation at the retina to process everything Selection is achieved partially through use of the fovea Remember the magnification in the cortex? The argument for mentioning the fovea here is strengthened by explaining that the rest of the retina can then act to signal what might be important in the environment, at which point, the person can move the eye to use the fovea to determine the details of the stimulus. The instructor can also mention the magnification factor of the fovea here since this indicates the importance of processing due to the amount of neural tissue that is responsible for this process.The argument for mentioning the fovea here is strengthened by explaining that the rest of the retina can then act to signal what might be important in the environment, at which point, the person can move the eye to use the fovea to determine the details of the stimulus. The instructor can also mention the magnification factor of the fovea here since this indicates the importance of processing due to the amount of neural tissue that is responsible for this process.

6. How is Selective Attention Achieved? Scanning a scene - eye movements can take in different parts of a scene Measuring eye movements - camera-based eye trackers show: Saccades - small, rapid eye movements Fixations - pauses in eye movements that indicate where a person is attending Approximately 3 fixations per second

7. Find the blonde lady with the pink shirt and sunglasses

10. Solving this task� There is too much incoming stimulation at the retina to process everything Selection is achieved partially through use of the fovea Scanning a scene - eye movements can take in different parts of a scene Measuring eye movements - camera-based eye trackers show: Saccades - small, rapid eye movements Fixations - pauses in eye movements that indicate where a person is attending Approximately 3 fixations per second

11. The next example is quite opposite� �and also would include a tremendous amount of practice�.and skill too!!

12. The �no look� Pass Dribbling down court (attending to: feet, court, boundary lines, bouncing ball,�etc) Paying attention to teammate off to the side Throwing a dead on pass without looking

13. Solving this task� There is too much incoming stimulation at the retina to process everything Selection is achieved partially through use of the fovea Scanning a scene - eye movements can take in different parts of a scene Measuring eye movements - camera-based eye trackers show: Saccades - small, rapid eye movements Fixations - pauses in eye movements that indicate where a person is attending Approximately 3 fixations per second

14. �this would also include Practice to the point where you could make the pass WITHOUT fovea mediated vision The �no look� is meant to fake out an opponent The pass is made using peripheral vision which would lack detail and information This support a role for attention in visual processing

15. William James 1890 Millions of items are present to my senses which never properly enter my experience. Why? Because they have no interest for me. My experience is what I agree to attend to�Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one of what seem several simultaneously possible objects or trains of thought�It implies withdrawal from some things in order to deal effectively with others.

17. Scanning a Scene Saccades- rapid eye movements punctuated by pauses The eye pauses to take in information from a scene Fixations- where a person is attending Typically we make about 3 fixations per second What determines where we fixate?

18. What Determines Location of Fixations? Characteristics of the scene: Stimulus salience - areas of stimuli that attract attention due to their properties Color, contrast, and orientation are relevant properties Saliency maps show fixations are related to such properties in the initial scanning process Bottom-up process that is unrelated to meaning Instructor may want to remind students of top-down versus bottom-up processing and what these terms mean.Instructor may want to remind students of top-down versus bottom-up processing and what these terms mean.

19. What Determines Location of Fixations? Bottom-up process that is unrelated to meaning Capturing attention by stimulus salience Attention is attracted by stimulus properties The pattern of stimulation falling on receptors is more important then the meaningfulness of the stimuli Instructor may want to remind students of top-down versus bottom-up processing and what these terms mean.Instructor may want to remind students of top-down versus bottom-up processing and what these terms mean.

20. Figure 6.5 (a) A visual scene. (b) Salience map of the scene determined by analyzing the color, contrast, orientations in the scene. Lighter areas indicate greater salience. (Reprinted from Vision Research, 42, Parkhurst, D., Law, K., & Niebur, E., Modeling the Role of Salience in the Allocation of Overt Visual Attention, 107-123 (2002).)

21. Characteristics of the Scene Picture meaning and observer knowledge Scene schema - prior knowledge about what is found in typical scenes Fixations are influenced by this knowledge Influence of the observer�s task Task demands override stimulus saliency Eye movements are usually preceded by motor movements by fraction of a second Instructor can note that predictions can be made more easily about location of fixations than order of fixations across people.Instructor can note that predictions can be made more easily about location of fixations than order of fixations across people.

22. Figure 6.6 Sequence of fixations of a person making a peanut butter sandwich. The first fixation is on the loaf of bread. (From Lord & Hayhoe, 2001.)

23. Home field advantage Home teams hope that fans will �distract� opponents from task demands to stimulus saliency Focus of athletes Foul shots

24. When Can Perception Occur Without Attention? Observers are shown scene very briefly Perceive �gist� of scene but no details You will see the next slide for 100 ms What will you see??

26. What did you see? How many drinks did you see? What fruits did you see? What was on the plate? What were the colors of the houses in the background? What color was the coaster? What else was on the table?

27. When Can Perception Occur Without Attention? Observers are shown scene very briefly Perceive �gist� of scene but no details Experiment by Li et al. Observers focused on center of display where 5 letters were flashed Task was to decide whether letters were same or different

28. Experiment by Li et al. A photograph of a scene was flashed in the periphery for 27 ms followed by a mask Position of scene moved for each trial Duration of scene was too short for eye movements to occur Observers could tell whether an animal was in the scene 76% of the time

29. Figure 6.7 Stimulus similar to those used by Li et al. (2002). See text for procedure.

30. When Is Attention Necessary for Perception? Inattentional blindness - a stimulus is not perceived even when the person is looking directly at it Experiment by Simons and Chabris Observers are shown short film of teams passing a basketball Task is to count number of passes Either a woman or person in gorilla suit walks through the teams 46% of observers fail to report the woman or gorilla

31. Figure 6.8 Inattentional blindness experiment. (a) Participants judge whether the horizontal or vertical arm is larger on each trial. (b) After a few trials, a geometrical object is flashed, along with the arms. (c) Then the participant is asked to pick which geometrical stimulus was presented. This slide can be used to talk about a second more controlled experimental procedure that shows inattentional blindness.This slide can be used to talk about a second more controlled experimental procedure that shows inattentional blindness.

32. When Is Attention Necessary for Perception? - continued Change blindness Observers were shown a picture with and without a missing element in an alternating fashion with a blank screen Results showed that the pictures had to alternate a number of times before the change was detected When a cue is added to show where to attend, observers noticed change more quickly Instructor can note that this effect can be seen with videos too. It is also important to note that people predict that they will be able to notice the changes, even when they are not able to do so. This effect was termed �change blindness blindness�, which is presented in the slide after the next one.Instructor can note that this effect can be seen with videos too. It is also important to note that people predict that they will be able to notice the changes, even when they are not able to do so. This effect was termed �change blindness blindness�, which is presented in the slide after the next one.

33. When Is Attention Necessary for Perception? - continued Change blindness blindness People are �blind� to the fact that they experience change blindness Past experience shows people that they do notice sudden changes In the real world motion is usually involved This usually is the signal that something changed

34. When Is Attention Necessary for Perception? - continued Disrupting attention leads to missing changes By looking at one picture then a blank screen and then another picture attention has been disrupted Continuity mistakes in movies although involving motion change from one scene to another (attention has been disrupted)

45. Figure 6.13 (a) Scene with blur added to simulate the decrease in visual acuity that occurs in the periphery of the visual field. The fixation point is on the woman�s face. (b) The same scene without blur. Even though our ability to see details is poor in the periphery, we generally experience the world as being �sharp� rather than blurry. (Blurring courtesy of Stuart Anstis.) This slide can be used to finish up the topic of change blindness by noting that even though our visual experience is that our view of the world is sharp and in focus, in reality the periphery is not. We function quite well this way.This slide can be used to finish up the topic of change blindness by noting that even though our visual experience is that our view of the world is sharp and in focus, in reality the periphery is not. We function quite well this way.

46. Effect of Attention on Information Processing Experiment by Posner et al. Observers saw a square with two lights on each side Precueing was used to indicate on which side the light would turn on Lights turned on consistent or inconsistent with the cue Task was to push button when light was seen Important to note that the observer fixates on the square with eyes.Important to note that the observer fixates on the square with eyes.

47. Experiment by Posner et al.  Results showed that observers responded fastest when cue was consistent with light Information processing is most efficient where attention is directed

48. Figure 6.14 (a) Posner et al.�s (1980) precueing procedure, a cue signal inside the square indicates where the light will be flashed. (b) Then one of the lights is illuminated.

49. Effect of Attention on Information Processing - continued Experiment by Egly et al. Observer views two rectangles Cue signals where target may appear Task was to press button when target appeared Results show: Fastest reaction time at targeted position �Enhancement� effect for non-target within the target rectangle Important to note that the enhancement effect occurs even when the distance from non-targets within and without the rectangle is the same. Thus, there is an �advantage� for targets within an object that is not related to any type of scanning of the eyes.Important to note that the enhancement effect occurs even when the distance from non-targets within and without the rectangle is the same. Thus, there is an �advantage� for targets within an object that is not related to any type of scanning of the eyes.

50. Figure 6.15 In Egly et al.�s (1994) experiment, (a) a cue signal appears at one place on the display, then (b) a target is flashed. Numbers are reaction times in ms for positions A, B, and C, when the cue appeared at position A.

51. Effects of Attention on Perception Experiment by Carrasco et al. Observers saw two grating stimuli with either similar or different contrast between the bars Task was to fixate on center point between gratings and indicate orientation of bars with higher contrast Small dot was flashed very quickly on one side before gratings appeared Important to note that the dot was flashed so quickly (160 ms) that attention could shift but that there could be no eye movement.Important to note that the dot was flashed so quickly (160 ms) that attention could shift but that there could be no eye movement.

52. Experiment by Carrasco et al. Results showed that: When there was a large difference in contrast, the dot had no effect When the contrast was the same, observers were more likely to report that the grating preceded by the dot had higher contrast Thus the shift of attention led to an effect on the perception

53. Figure 6.17 (a) Stimuli to measure how attention might affect perception. (b) Stimuli used by Carrasco et al. (2004). Note that this slide shows the original stimuli used for experiments of how attention might affect perception. With this procedure, observers were told to pay attention to one stimulus and report if it was brighter than the other, non-attended stimulus. However, there was the problem that the observer could expect that paying attention to the stimulus should make that stimulus stand out more, which might lead him or her to report that the attended stimulus was brighter, when the two stimuli actually appear to be equally bright. The procedure by Carrasco eliminates this potential bias. Note that this slide shows the original stimuli used for experiments of how attention might affect perception. With this procedure, observers were told to pay attention to one stimulus and report if it was brighter than the other, non-attended stimulus. However, there was the problem that the observer could expect that paying attention to the stimulus should make that stimulus stand out more, which might lead him or her to report that the attended stimulus was brighter, when the two stimuli actually appear to be equally bright. The procedure by Carrasco eliminates this potential bias.

54. William James 1890 Millions of items are present to my senses which never properly enter my experience. Why? Because they have no interest for me. My experience is what I agree to attend to�Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one of what seem several simultaneously possible objects or trains of thought�It implies withdrawal from some things in order to deal effectively with others.

55. What Attention Does Attending to an object brings it to the forefront of our consciousness and may even alter its appearance (previous example) Not attending to an object can cause us to miss it altogether

56. Attention and Experiencing a Coherent World Binding - process by which features are combined to create perception of coherent objects Binding problem - features of objects are processed separately in different areas of the brain So, how does binding occur?

57. Figure 6.18 Any stimulus, even one as simple as a rolling ball, activates a number of different areas of the cortex. Binding is the process by which these separated signals are combined to create a unified percept.

58. Feature Integration Theory Treisman and Gelade Preattentive stage - features of objects are separated Focused attention stage - features are bound into a coherent perception Attention serves as the �glue� between the physiology of the what and where streams Note that this stage theory focuses on BEHAVIOR in the sense that attention is required to complete the perceptual process, but that it also includes the basic physiology as well. What stream = information about features such as color and form. Where stream = information about location and motion.Note that this stage theory focuses on BEHAVIOR in the sense that attention is required to complete the perceptual process, but that it also includes the basic physiology as well. What stream = information about features such as color and form. Where stream = information about location and motion.

59. Figure 6.19 Flow diagram of Treisman�s (1988) feature integration theory.

60. Figure 6.20 (a) A single object. Binding features is simple in this case because all of the features are at one location. (b) When multiple objects with many features are present, binding becomes more complicated. Triesman�s theory states that binding occurs with multiple objects by focusing attention on each object in turn. Triesman�s theory states that binding occurs with multiple objects by focusing attention on each object in turn.

61. Illusory Conjunctions Features that should be associated with an object become incorrectly associated with another Experiment by Triesman & Schmidt Stimulus was 4 shapes flanked by 2 numbers Display flashed briefly followed by a mask Task was to report numbers first followed by shapes at 4 locations Additional evidence for Treisman�s theory.Additional evidence for Treisman�s theory.

62. Figure 6.21 Stimuli for Treisman and Schmidt�s (1982) illusory conjunction experiment.

63. Illusory Conjunctions - continued Results showed that: Incorrect associations of features with objects occurred 18% of the time Asking observers to focus on the target objects eliminated this effect Balint�s syndrome - patients with parietal lobe damage show lack of focused attention results in incorrect combinations of features

65. Balint�s syndrome Patients suffering from this syndrome produce inaccurate reaching movements towards a target or object in space, this is especially true with their contralesional hand � The kinematics of their reach is also altered, the reach takes longer with a lower velocity and a longer deceleration phase Grasping of objects is also impaired, correctly orientating the hand and inadequate pre-shaping with respect to the target occurs� The patient's performance is even more severely deteriorated when vision of either the hand or the target is prevented (Kolb & Whishaw, 1996)�

66. Visual Search Conjunction search - finding target with two or more features Patients with parietal lobe damage cannot perform conjunction searches well compared to people without such damage Parietal lobe is the destination for the where stream

67. Figure 6.22 Find the horizontal green line in (a) and then in (b). Method - Searching for conjunctions (This material is from the text but can be used to do the demo in class.) We can understand what a conjunction search is by first describing another type of search called a feature search. Before reading further, look at Figure 6.22, and find the horizontal line in (a) and then in (b). The search you carried out in Figure 6.22a was a feature search because the target can be found by looking for a single feature - �horizontal.� In contrast, the search you carried out in Figure 6.22b was a conjunction search because it was necessary to search for a combination (or conjunction) of two or more features on the same stimulus. In Figure 6.22b, you couldn�t focus just on green because there are vertical green lines, and you couldn�t focus just on horizontal because there are horizontal red lines. You had to look for the conjunction of horizontal and green.Method - Searching for conjunctions (This material is from the text but can be used to do the demo in class.) We can understand what a conjunction search is by first describing another type of search called a feature search. Before reading further, look at Figure 6.22, and find the horizontal line in (a) and then in (b). The search you carried out in Figure 6.22a was a feature search because the target can be found by looking for a single feature - �horizontal.� In contrast, the search you carried out in Figure 6.22b was a conjunction search because it was necessary to search for a combination (or conjunction) of two or more features on the same stimulus. In Figure 6.22b, you couldn�t focus just on green because there are vertical green lines, and you couldn�t focus just on horizontal because there are horizontal red lines. You had to look for the conjunction of horizontal and green.

68. Table 6.1 This slide can be used to summarize the material that was just presented on illusory conjunctions and conjunction searches.This slide can be used to summarize the material that was just presented on illusory conjunctions and conjunction searches.

69. Physiological Approach to Binding Synchrony hypothesis - neurons firing to same object synchronize with each other The firing of the neurons shows the same pattern (not at the same time) Synchrony may also occur between neurons firing for different qualities of the same object Attention may help synchronize neural firing Important to note that this is not a well accepted hypothesis.Important to note that this is not a well accepted hypothesis.

70. Figure 6.23 How synchrony can indicate which neurons are firing to the same object. Each circle represents a cortical neuron that fires to a specific orientation of the woman (blue) or dog (red). (Based on Engel et al., 1999.)

71. The Physiology of Attention Experiment by Colby et al. Monkey trained to keep eyes fixated on a dot while peripheral light was flashed on the right Task in �fixation only� condition: Keep eyes fixated and release lever when dot dimmed Task in �fixation and attention� condition: Keep eyes fixated and release lever when peripheral light dimmed

72. Experiment by Colby et al. Recordings from a neuron in the parietal lobe that responded to the peripheral light were made while monkey did task Neuron responded well when monkey was attending to peripheral light Neuron responded poorly when monkey was not attending to it Important to note that response was due to attention since the eyes were always fixated on dot Note that similar results have been found in other single cell recording experiments with animals as well as brain imaging experiments with people.Note that similar results have been found in other single cell recording experiments with animals as well as brain imaging experiments with people.

73. Do Neurons Notice Stimuli? Experiment by Sheinberg & Logothetis Monkey was trained to pull lever different directions for specific objects Recorded from IT neurons in monkey�s cortex that responded to specific objects Recordings showed response to both single object and to object placed in a scene When monkey scanned a scene containing the target objects, the neuron only fired when monkey noticed the object The important element here is that is it not enough simply to look at the object, but it must be noticed in order for certain neurons to respond. The instructor could also talk about feature detectors here again and reference the earlier material on this topic.The important element here is that is it not enough simply to look at the object, but it must be noticed in order for certain neurons to respond. The instructor could also talk about feature detectors here again and reference the earlier material on this topic.