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
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.
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.

5. 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 three fixations per second

6. Figure 6.3 A person looking at a stimulus picture in a camera-based eye tracker. Reprinted from Trends in Cognitive Science, 7, Henderson, John M., , (2003), with permission from Elsevier.)

7. 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.

8. 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 and fixations are closely linked to the action the person is about to take.
Instructor can note that predictions can be made more easily about location of fixations than order of fixations across people.

9. Figure 6.6 Sequence of fixations of a person making a peanut butter sandwich. The first fixation is on the loaf of bread. From Land, M. F., & Hayhoe, M. (2001.) In what ways do eye movement contribute to everyday activities? Vision Research, 41,

10. Effects of Past Experience
Experiment by Shinoda et al.
Observers’ fixations were measured during computer simulated driving.
They were more likely to detect stop signs when they were at intersections.
People have learned that this is where stop signs are typically placed.

11. Perception can Occur Without Focused Attention
Experiment by Reddy et al.
Observers performed one of three tasks
Central task - determine whether letters flashed in the center of the screen are the same
Peripheral task - determine whether faces flashed to the side of the screen are male or female
Dual task - do the same as the peripheral task and determine the color of a disc

12. Experiment by Reddy et al. - continued
Performance in the single task condition was 80 to 90%.
Performance in the dual task condition was 90% for faces, and 54% for the discs.
Results show that the gender of a face can be determined without focused attention while the disc identification could not be made.
Faces have meaning and are perceived as whole objects.

13. Perception can be Affected by a Lack of Focused Attention
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 with an umbrella or a person in gorilla suit walks through the teams.
46% of observers fail to report the woman or gorilla.

14. This slide can be used to talk about a second more controlled experimental procedure that shows inattentional blindness.
Figure 6.9 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.

15. Perception can be Affected by Lack of Focused Attention - 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.

16. When Is Attention Necessary for Perception? - continued
Change blindness also occurs for film shots.
People are “blind” to the fact that they experience change blindness.
Real objects in the environment change with some type of movement, which is why we normally don’t experience change blindness.

17. Does Attention Enhance Perception?
Experiment by Posner et al.
Observers looked at a fixation point.
Precueing with an arrow indicated on which side a stimulus was likely to appear.
Stimuli appeared that were consistent (valid trial) or inconsistent (invalid trial) with the cue.
Task was to push button when a target square was seen.
Important to note that the observer fixates on the + with eyes and does not move them during the trials.

18. Experiment by Posner et al. - continued
Results showed that observers responded fastest on valid trials.
Posner believed these results showed that information processing is most efficient where attention is directed.

19. Figure 6.14 Procedure for (a) the valid task and (b) the invalid task in Posner et al.’s (1978) precueing experiment. See text for details; (c) The results of the experiment: average reaction time was 245 ms for valid trials but was 305 ms for invalid trials.

20. Does Attention Enhance Perception? - 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 eye scanning.

21. 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 at one of four possible locations, A, B, C, or D. Numbers are reaction times in ms for positions A, B, and C, when the cue appeared at position A.

22. 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.

23. Experiment by Carrasco et al. - continued
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 perception

24. Note that this slide shows the original stimuli used for experiments of how attention might affect perception in (a). 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 shown in (b) by Carrasco (that was presented in the previous slide) eliminates this potential bias.
Figure 6.17 (a) Stimuli to measure how attention might affect perception. (b) Stimuli used by Carrasco et al. (2004).

25. 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?

26. 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.

27. 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.

28. Figure 6.19 Flow diagram of Treisman’s (1988) feature integration theory.

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

30. Figure 6.21 Stimuli for Treisman and Schmidt’s (1982) illusory conjunction experiment.

31. 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

32. 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.

33. We can understand what a conjunction search is by first describing another type of search called a feature search. 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.
Figure 6.22 Find the horizontal line in (a) and then the green horizontal line in (b).

34. Physiological Approach to Binding
Synchrony hypothesis - neurons firing to same object synchronize with each other
The firing of the neurons shows the same pattern.
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.

35. Figure 6.23 How synchrony can indicate which neurons are firing to the same object. See text for explanation. Based on Engel A. K., Fries, P., Konig, P., Brecht, M., & Singer, W. (1999). Temporal binding, binocular rivalry, and consciousness. Consciousness and Cognition, 8,

36. The Physiology of Attention
Experiment by Colby et al.
Monkey trained to keep eyes fixated on a fixation light (Fix) while stimulus light was flashed on the right
Task in “fixation only” condition:
Keep eyes fixated on Fix and release lever when Fix dimmed
Task in “fixation and attention” condition:
Keep eyes fixated on Fix and release lever when stimulus light dimmed

37. Experiment by Colby et al.
Recordings from a neuron in the parietal lobe that responded to the stimulus light were made while monkey did task.
Neuron responded well when monkey was attending to stimulus light.
Neuron responded poorly when monkey was not attending to it.
It is important to note that response was due to attention since the eyes were always fixated on Fix.
Note that the stimuli (both the stimulus light and the fixation point) were always the same on the monkey’s retina. Note also that similar results have been found in other single cell recording experiments with animals as well as brain imaging experiments with people.

38. Figure 6. 24 The results of Colby et al
Figure 6.24 The results of Colby et al.’s (1995) experiment showing how attention affects the responding of a neuron in a monkey’s parietal cortex. The monkey always looked at the dot marked “Fix”. A stimulus light was flashed within the circle off to the side. (a) Nerve firing when the monkey was not paying attention to the light. (b) Nerve firing when the monkey was paying attention to the light. Reprinted from Colby,C. L., Duhamel, J. R., & Goldberg M. E., Oculocentric spatial representations in parietal cortex. Cerebral Cortex, 5, 1995, Copyright © 1995, with permission from Oxford University Press.

39. 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 the 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.

40. Figure 6.26 Bottom: graph showing how far the monkey’s gaze was from the parrot. Notice that the neuron begins firing just after the monkey has fixated on the parrot (arrow) and shortly after this the monkey pulls the lever (vertical line). From Sheinberg, D. L., & Logothetis, N. K. (2001). Noticing familiar objects in real world scenes: The role of temporal cortical neurons in natural vision. Journal of Neuroscience, 21,

41. Attention and Autism
A major symptom of autism is withdrawal from contact with people.
People with autism can solve reasoning problems about social situations, but cannot function when placed in these situations.
Experiment by Klin et al.
Participants were autistic and nonautistic people.
Watched movie while eye fixations were tracked

42. Experiment by Klin et al. - continued
Results for nonautistic observers showed:
Looked at eyes of actors to determine emotional state
Looked in the direction a person pointed and then at the face of the person who should reply
Autistic observers look at socially irrelevant stimuli in these situations.
Thus, where autistic individuals pay attention in a social situation may lead to perceiving the world differently.

43. Figure 6.27 Where people look when viewing this image from the film Whose Afraid of Virginia Woolf? Nonautisitic viewers: white crosses; autistic viewers: black crosses. From “The Enactive Mind, or From Actions to Cognition: Lessons from Autism,” by A. Klin, W. Jones, R. Schultz, & F. Wolkmar, Philosophical Transactions of the Royal Society of London B, pp Copyright The Royal Society. Published online.

44. Figure 6.28 Scan paths for nonautistic viewers (white path) and autistic viewers (black path) in response to the picture and dialogue while viewing this shot from Whose Afraid of Virginia Woolf? From “The Enactive Mind, or From Actions to Cognition: Lessons from Autism,” by A. Klin, W. Jones, R. Schultz, & F. Wolkmar, Philosophical Transactions of the Royal Society of London B, pp Copyright The Royal Society. Published online.

45. Neural Processes for Attention in Autism
Experiment by Pelphrey et al.
Measured responses in the STS
Nonautistic and autistic participants watched an animated character that:
moved eyes toward a checkerboard (congruent condition).
moved eyes away from a checkerboard (incongruent condition).
STS = superior temporal sulsus -- an area in the temporal lobe that has been shown to be sensitive to how other people direct their gaze in social situations. For example, it is strongly activated in cases when a passerby makes eye contact with the person.

46. Experiment by Pelphrey et al. - continued
Observers pressed a button when they saw the character’s eyes move.
All participants performed at 99% accuracy.
But, activation of the STS for nonautistic people was higher in the incongruent condition.
Autistic people showed equal activation in both conditions.
Results suggest that autistic people cannot read intentions of others.

47. Figure 6.29 (b) Response of the STS in autistic and nonautistic observers to the two conditions, C = congruent; IC = incongruent. From Pelphrey, K. A., Morris, J. P., & McCarthy, G. (2005). Neural basis of eye gaze processing deficits in autism, Brain, 128,