Chapter 3 - Practice Questions

3.12 What advantages has parallel processing over serial processing?

Whereas in serial processing one step can only be initiated when the last step is completed, many different steps are performed simultaneously in parallel processing, which results in greater speed. Moreover, the different steps or analyses can inform each other in parallel processing, which is not feasible in serial processing.

3.9 (XX) Use the Mach bands illusion to describe the process of edge enhancement

Edge enhancement is produced by lateral inhibition, or in other words, the process by which a neuron's activity inhibits the activity of its neighbors and vice versa. In the Mach band illusion a neuron at the transition to the next strip receives less inhibition from a neuron detecting the darker left strip (due to less stimulation)letting the left edge of the next strip appear brighter than the rest of it.

3.2 Which three Gestalt principles are associated with these figures, and describe how we perceive the figures, and how we would perceive them if the Gestalt principles don't hold.

A) Priniciple of similarity. We tend to group these dots into columns rather than rows, using the dots' colours as a grouping characteristic. If this principle would not hold, we might see 16 individual dots. B) Principle of good continuation. We tend to see a continuous green bar, that is hidden behind the orange pillar, rather than two smaller rectangles next to the pillar which we might perceive if this principle does not hold. C) Principle of simplicity. We tend to interpret a form in the simplest way possible. Instead of perceiving a 12-sided polygon, the principle of similarity causes us to see two intersecting rectangles.

3.14 Which two Gestalt principles of organization are depicted below? Describe how we perceive the figures, and how the Gestalt princple influences this process.

A) illustrates the principle of closure. We perceive a circle and a square, revealing our bias to toward perceiving closed figures rather than incomplete ones. B) Illustrates the principle of proximity. We tend to perceive groups, linking dots that are close together

Which sense is dominant in humans, and provide two arguments supporting this view (and provide an example)

According to the book, vision is the dominant sense in humans. This is firstly based on the percentage of brain area that is devoted to vision compared to brain area used for the other senses. Secondly, the significance of vision is evident in human behaviour: When information from different senses is conflicting, the visual input is dominant. An example of visual dominance can be found in the McGurk effect, where the visual input influences the perception of an auditory stimulus.

3.4 Describe an example that demonstrates that the detection of features, an early phase in visual perception, is influenced by higher level interpretation.

An example that shows the influence of higher level interpretation are words of which one can only "see" the shadows of the letters ("PERCEPTION" in the book). Although the features of the letters are not present, we still "perceive" them by filling in the blanks based on a global analysis of the presented stimulus.

3.6 (XX) Which part of the retina enables color perception? Explain how color perception works.

Cones are the type of photoreceptor which is sensitive to color differences. There are three sorts of cones, each one being sensitive to a different wavelength. Perceiving a certain color results from a comparison of the output from all three sorts of cones.

3.7 (XX) Why do persons point their eyes toward targets they would like to perceive in detail?

Due to the high density of cones near the fovea and the cones' high acuity, persons point their eyes directly to the target so that its image falls onto the fovea, the area of the retina with the greatest acuity.

3.8 Which process is essential for perceiving an object's boundaries?

Edge enhancement

3.13 (XX) Name three elements which contribute to solving the binding problem.

Firstly, spatial position provides a reference for the reassembly of the different parts of an object or scene. Secondly, rhythm is used by the brain to determine which elements belong together. Synchronous neural firing signals that two elements are part of the same object. Thirdly, attention is needed to achieve neural synchrony.

3.17 (XX) The artist Leon Keer creates 3D street paintings. When viewed from the right angle (see picture A), the illusion is powerful. Looking at the painting from a different angle, it appears distorted (see picture B). Name the different cues of depth which are used by the artist to create the illusion of 3D

Interposition, light and shadow, distance cues, linear perspective

3.15 Why is the statement that "perception can be divided into an information gatheringstep followed by an interpretation step" plausible, but nonetheless wrong?

It is plausible because one might assume that the first step in perception consists of collecting information about the stimulus, such as the single corners and angles. Afterwards, the second step consists of interpreting the collected "raw data" or in other words, "going beyond the information given". This sequence of actions resembles serial processing. However, the brain's functioning however relies on parallel processing, analyzing a figure's basic features and the figure's large-scale configuration simultaneously. Neither type of processing is prioritized. This allows for interaction between both processes, guiding the perception of features by the configuration, and informing the analysis of the configuration by the features. An example is Figure 3.15 in the 6th edition of the book, which after being reorganized, contains the features to recognize the letters of the word "Lift". Thus, features themselves depend on the form's organization by the viewer as the figure itself.

3.10(XX) Black light theatre exploits the human eye's failure to distinguish black objects from a black background. Use your knowledge about edge enhancement to explain how this failure comes about.

Object recognition necessitates to perceive an object's boundaries and ultimately its shape. Edge enhancement greatly contributes to define an object's shape. When a black object is displayed against a black background there is no edge enhancement since it depends on lateral inhibition. More specifically, lateral inhibition enhances the contrast in brightness that define an object's boundary, but without any contrast in brightness given, no edges are enhanced. Hence, the black object is not perceived against the black background

3.3 Using one of the two images, explain the statement "perception is not neutral".

Perception is not neutral because the perceiver adds an interpretation to the input he/she is getting. Both images displayed here are reversible, or bistable, which means that they provide for two prominent and stable interpretations of the visual features. A) The Schroeder staircase can either be perceived as a right-side-up set up stairs as if looking from underneath, or as an upside-down set as if looking on top of the stairs. B) In the Canadian flag one can either see the white part as a stencil lying on top of a red background, or the red parts to be lying on top of a white background. Thus, perception involves some interpretation of the visual input and is therefore not "neutral".

3.11 (XX) What does it mean to say that the visual system relies on a "divide and conquer strategy"?

The "divide and conquer" strategy refers to the division of analysis of the visual input. Certain cell types only respond to a specific input, such as an object's orientation. Together the different cells, located in different parts of the cortex, achieve visual perception.

3.18 (XX) Explain why the visual system relies on many different cues which do provide the same information

The redundancy of distance cues ensures flexibility and versatility of the visual system. Since not every cue is available in every circumstance, for instance binocular disparity can only be used for close objects, alternative cues are needed in order to provide the visual system with distance information.

3.5 (XX) Name the three layers of which the retina is composed.

The retina is composed of the rods and cones, also referred to as the photoreceptors, the bipolar cells and the ganglion cells.

3.16(XX) Name two factors contributing to size constancy.

The unchanging relationships of objects within the retinal image is one contributing factor. Another is unconscious inference, which uses the relationship between an object's distance and retinal image size.