Sensation & Perception, 4e

Chapter 7 Study Questions


1. What is attention?

Answer: Attention is a single term that refers to many different functions. It is any of a large set of selective processes in the brain. To deal with the impossibility of handling all inputs at once, the nervous system has evolved mechanisms that are able to bias processing to a subset of things, places, ideas, or moments in time. At its heart, attention is the differential processing of some stimuli and not others.

Selection in Space

2. Describe the idea behind the cueing paradigm.

Answer: This paradigm measures how fast a subject responds to a target appearing in one of two or more locations under various cueing conditions in order to infer how attention affects performance. Generally, there is a “valid cue,” an “invalid cue,” and a “neutral cue.” A valid cue signals the correct location where the target will appear, while an invalid cue signals the wrong location. A neutral cue is uninformative. The idea is that when an invalid cue is given, the observer will take longer to respond to the appearance of the target than when a valid cue is given. A neutral cue will result in a response that is slower than the valid cue case but quicker than the invalid cue case. This demonstrates that responses to a target depend on prior attention to locations in the visual field.

3. What is the “spotlight” theory of attention?

Answer: It is a metaphor for attention based on the idea that attention can be moved from location to location in a manner similar to that of a spotlight. An elaboration on the spotlight model is the notion of a “zoom lens” which reflects the idea that attention may grow or shrink to encompass stimuli or regions of different sizes in the visual field.

Visual Search

4. How are visual search experiments useful for studying attention?

Answer: Visual search experiments provide a reasonable approximation of attention in the real world. The typical visual search experiment requires the observer to find a “target” item among some number of “distractor” items. This kind of search occurs regularly in the real world. For instance, looking for faces in a crowd, books on a shelf, etc.

5. Explain how a search can be inefficient.

Answer: When the target and distractors in a visual search task contain the same basic features, the search is inefficient. For example, if all the distractors in the task contain the color blue, and the target also contains the color blue, a search can be inefficient in that the observer may have to go through each item in the display in order to locate the target. This is contrasted with a situation in which the target stands out from the distractors, and as a result the observer does not need to attend to each stimulus in the display.

6. Describe one type of visual search that is efficient.

Answer: Feature search is an example of an efficient kind of visual search. In this case, the target is defined by a single attribute such as a salient color or orientation. For instance, imagine having to search for a red car in a parking lot full of white cars. The defining feature (red) is sufficiently salient, and it does not matter how many cars are in the parking lot. The red car stands out in the display. In this situation, we process the colors of all of the cars at once, or in parallel, making the search efficient.

7. Why is conjunction search less efficient than feature search?

Answer: Conjunction search is less efficient than feature search because conjunction search requires combining two or more attributes to locate a target (e.g., a blue, horizontal target among blue vertical and green horizontal distractors), as opposed to feature search, which only requires searching for a target defined by a single attribute.

8. What is guided search?

Answer: Guided search is the idea that attention can be restricted to a subset of possible items on the basis of information about the target item’s basic features, like its color, shape, size, or orientation.

9. What is the binding problem?

Answer: The binding problem is the challenge of tying different attributes of visual stimuli (e.g., color, orientation, motion), which are handled by different brain circuits, to the appropriate object so that we perceive a unified object (e.g., red, vertical, moving right).

10. Describe Treisman's feature integration theory.

Answer: This theory of visual attention states that a limited set of basic features can be processed in parallel preattentively, but that other properties, including the correct binding of features to objects, require attention.

11. How are illusory conjunctions a by-product of conjunction search?

Answer: An illusory conjunction is an erroneous combination of two preattentive features in a visual scene. For instance, seeing a red X when the display contains red Ys and blue Xs, but no red Xs. This error can occur during a recognition task that involves conjunction search, when the observer tries to report which objects were present in a display of items. The observer mistakenly binds attributes of one object with attributes of another.

12. What are the two stages of feature integration theory?

Answer: The two stages of feature integration theory are: 1) The preattentive stage, which refers to the processing of stimuli that occurs before selective attention is deployed to any particular stimulus; and 2) The attentive stage, which refers to processing that requires the deployment of attention to a particular stimulus or location.

Attending in Time: RSVP and the Attentional Blink

13. Describe one phenomenon where timing is critical to visual attention.

Answer: One such phenomenon is known as the “attentional blink.” In this case, there is a difficulty in perceiving and responding to the second of two target stimuli amid a rapid stream of distracting stimuli if the observer has responded to the first target stimulus within 200 to 500 ms before the second stimulus is present.

The Physiological Basis of Attention

14. What is attentional selection, and why is it important?

Answer: Attentional selection is the ability to attend to specific properties of a display, which may require switching attention from other properties without moving the eyes. This ability is important because it allows one to focus on the relevant information in a display rather than “getting lost” in the entire display. During attentional selection, different aspects of the display appear more prominent as one shifts attention to the property selected.

15. What do fMRI studies involving the fusiform face area demonstrate about attention?

Answer: These studies show that attentional selection can be used to perform one type of specialized processing rather than another. One study showed that the fusiform face area is especially important in the processing of faces and that the parahippocampal place area is especially important in the processing of places. If observers view an image of a face superimposed over an image of a house, the face area becomes more active when the observer is attending to the face, and the place area becomes more active when the observer is attending to the house.

16. How is response enhancement related to attentional processing on the cellular level?

Answer: Response enhancement of single cells is one of the ways in which attention could change the response of a cell. For instance, a cell that responds to a specific orientation (e.g., vertical) might give a stronger response in the presence of attention.

17. Describe sharper tuning and its relevance to attentional processing.

Answer: Sharper tuning is one possible effect of attention on the response of neurons. Attention might cause a neuron to respond more precisely. For instance, a neuron that normally responds to lines with orientations from –20° to +20° might come to respond to ±10° lines instead.

18. Describe the notion of altered tuning at the cellular level in response to attention.

Answer: Altered tuning refers to the idea that cells in visual cortex might change their receptive field properties to process features of objects to which the organism is attending. For instance, in Figure 7.22 the receptive field of neurons shifted from one object to another depending on which item was being attended at that time.

Disorders of Visual Attention

19. What is neglect?

Answer: Neglect is a disorder of visual attention in which there is an inability to attend to or respond to stimuli in the contralesional visual field (typically the left visual field after a right parietal damage). Neglect can also involve half of the body or half of an object. The disorder seems to stem from an attentional processing problem rather than from a visual problem since the person with the disorder is not blind in the neglected hemifield.

20. How is extinction related to neglect?

Answer: Extinction might be neglect in a milder form. Extinction is the inability to perceive a stimulus in the presence of another stimulus, typically in a comparable position in the other visual field. Neglect is a more severe disorder, in which the entire contralesional field might be affected.

Perceiving and Understanding Scenes

21. Describe the difference between the selective and nonselective pathways.

Answer: Early visual processing feeds into two separate pathways—a selective and a nonselective pathway. The selective pathway passes through the bottleneck of attention and thus fully processes all of the features of one or a few objects at a time. The nonselective pathway does not pass through the attentional bottleneck and instead computes the ensemble statistics of a scene rather than the details of any particular objects.

22. What does it mean to compute the ensemble statistics of a scene?

Answer: The ensemble statistics of a scene are the distribution of properties such as orientation, size, or color over a set of objects. Importantly, the distribution of these properties is represented holistically—as an ensemble—giving the observer a global description of the entire scene rather than a local description of any of the particular elements in the scene. Such ensemble statistics can be used to quickly process important properties of the world, such as scene gist and spatial layout.

23. Explain how the flicker paradigm helps to examine the phenomenon of “change blindness.”

Answer: During the flicker paradigm, observers are given a picture memory experiment. First, they see a picture of a scene, then it vanishes for a split second, and then it is replaced by a similar image. The task is to determine what changed between the first and second images. The two images continue to flip back and forth (with a blank screen appearing between them) until the observer spots the change or time runs out. The results of this task show that observers are slow at detecting changes in a scene, referred to as “change blindness.” Change blindness indicates that despite the fact that our perception of the world seems rich and full of detail, we are actually only processing a very small number of objects at any given time.

24. Explain the notion of inattentional blindness.

Answer: Inattentional blindness refers to a failure to notice a stimulus or event because the observer is paying attention to other items in the visual field. The stimulus or event would typically be quite noticeable to the observer, if they weren’t occupied paying attention to something else.