Chapter 7

Question 1

FQ.1: How might sophisticated eyes like ours may have evolved from primitive beginnings?

Answer 1

• In some ancient animals, photoreceptors became concentrated in a spot under the skin.
• By developing through generations, they have developed the ability to react to shadows as well.
• The skin covering these eye-spots became transparent to enable clear vision and let in more light.
• These receptor accumulations then moved deeper, inside liquid filled cavities to reduce glare and enable the animal to detect the direction the light is coming from.
• One of the membranes covering the eye became thicker to form a lens. This lens later became capable of reflecting shapes and images onto the photoreceptors.
• Enhancement of eyes, along with proper nervous adaptations

Question 2

FQ.2: How do the cornea, iris, and lens help to form images on the retina?

Answer 2

• The cornea helps focus the light that passes through it.
• The iris, thanks to its muscle fibres, can change the diameter of the pupil, to let more or less light inside.
• The lens adds to the focusing process, but changes its shape depending on the distance of the focus to adapt better.

Question 3

FQ.3: How are cones and rods distributed on the retina, and how do they respond to light?

Answer 3

• Cones are more concentrated in the fovea area, where the reflection of vision primarily falls. Further from the fovea, their concentration decreases.
• Cones are specialised in vision in brightness;
• Rods exist everywhere in the retina except fovea.
• Rods detect vision in dim light.

Question 4

FQ.4: How do rod vision and cone vision differ?

Answer 4

• Cone vision allows us to have a bright and acute vision of our surroundings during day;
• Rod vision gives us a more vague vision but enables us to tell important details apart in dim light or darkness.

Question 5

FQ.5: What is the chemical basis for dark adaptation and light adaptation? Why do we see mostly with cones in bright light and with rods in dim light?

Answer 5

• Photochemical of rods, rhodopsin, are much more sensitive to light than photochemicals of cones. Intense light causes rhodopsin to break down, rendering the rods inactive. Therefore, we see entirely with cones in bright light.
• In dim light, rhodopsin regenerates in around 25 minutes to activate rods again and allow dark vision.
• Cone photochemicals go through the same process as well, but exhibit much, much smaller changes than that of rods.

Question 6

FQ.6: How does the trichromatic theory explain the three-primaries law? How was the theory
validated by the discovery of three cone types?

Answer 6

• Trichromatic theory argues that three different types of receptors are responsible for detecting light belonging to different portions of the wavelength spectrum.
• This theory would automatically affirm the three-primaries law (three primary light colors make up all colors we see)
• the theory, as well as the law are indeed correct, confirmed by the discovery of three different types of cone receptors which are responsible for detecting different wavelengths.

Question 7

FQ.7: Why does vision in some people obey a two-primaries law rather than the three-primaries law,
and why are these people not good at picking cherries? How does the color vision of most nonprimate
mammals, and that of most birds, differ from that of most humans?

Answer 7

• A defect in the gene responsible for the production of photochemicals can cause the lack of these chemicals, therefore to a condition called colour blindness.
• Most of these people have difficulty distinguishing
  colours ranging from green to red (500-700 nm) and therefore would not be able to distinguish red
  cherries among green leaves, relying on colour.
• Most nonprimate mammals have only two types of
  cones and have hardships at distinguishing upper wavelength colours.
• most birds have a fourth type of photoreceptor which allows them to see ultraviolet light since they rely heavily on sight during flight, hunting and feeling; their hatchlings have ultraviolet mouths so their parents can distinguish them from afar.

Question 8

FQ.8: How does the opponent-process theory explain (a) the law of complementarity in color mixing
and (b) the complementarity of afterimages?

Answer 8

• some colours – complementary ones, when mixed, won’t produce a new one but get paler and closer to white
• Hering attempted to explain this with physiological structures that are either inhibited or excited
  according to the wavelength; and complementary colours would produce opposite effects on these units.
• Color receptors get fatigued when looking at a stable image for a long time, and when the vision is
  directed onto a neutral surface – like a white sheet of paper – the fatigued receptor of a pair of complementary
  receptors does not respond immediately, causing us to see the negative coloured afterimage of the
  previous one; this creates the complementarity of afterimages.

Question 9

FQ.9: How has the opponent-process theory been validated in studies of the activity of neurons that
receive input from cones?

Answer 9

• Apparently the eye really contains three different types of cone cells, which reaffirms the first theory;
• however these cones feed into the ganglion cells in a pattern that translates the trichromatic code into
  an opponent-process code.
• Receptors that respond best to opposite colors feed into the same ganglion cells with opposite effects.

Question 10

FQ.10: How can you know what an infant sees? What methods can be used to determine visual acuity
in young babies?

Answer 10

• Babies have not fully developed the ability to accommodate their lenses, look with both eyes at the same focus or follow moving objects with their eyes; however they catch up to each and all of these
  adaptations within 6 months.
• Even before these dates, babies have been observed to react differently tonsufficiently different visual stimuli, and to look at it more when presented with a new one. These
  observations have led us to try babies’ visions with different patterns (bull’s eyes vs. checkerboards etc.)
  to see how they discriminate between them.

Question 11

FQ.11: What are experience-expectant processes, and how do they relate to the development of
vision?

Answer 11

• Infants of varying species are born with pre-set expectations as to what kind of stimuli they will receive;
  and they adapt and develop according to this stimuli.
• If these processes are not interrupted,
  the postnatal visual development is advanced and completed healthily.
• If they are deprived of necessary visual stimuli,
  they have visual impairments varying in degree of reversibility.

Question 12

FQ.12: What kinds of stimulus features influence the activity of neurons in the primary visual cortex?

Answer 12

The colour, shape, contouring, angle, movement and its relation to the background determine the
neurons that become activated.

Question 13

FQ.13: What is the difference between parallel processing and serial processing? What role does each
play in Treisman’s feature-integration theory of perception?

Answer 13

• Detection of features occurs through parallel processing.
• This occurs instantaneously and on all the
  stimulus array. Primitive individual features are picked up separately.
• The integration of features involves
  serial processing, which occurs sequentially, at one spatial area at a time. Attention to individual objects is necessary. Individually picked up features are joined together here.

Question 14

FQ.14: How do pop-out phenomena and mistakes in joining features provide evidence for Treisman’s
theory?

Answer 14

• Pop-out phenomena indicates parallel processing, which makes it easy to detect one single difference in
  primary features no matter how many distractors there are.
• However, when two or more features are
  joined and a single distinct object is the target, it takes longer to find it, which indicates that the joining
  of these features involve serial processing.
• Moreover, when people are presented with simple shapes for brief moments, they can memorise all the basic components; however they sometimes confuse which
  features belonged together to form a single object.
• This indicates that parallel processing can occur in
  such brief time but serial processing takes more time and conscious effort

Question 15

FQ.15: What are some principles of grouping proposed by Gestalt psychologists, and how does each help explain our ability to see whole objects?

Answer 15

• Principle of proximity describes our tendency to see accumulated objects as a part of a larger object.
• Principle of similarity involves stimulus elements that are similar or different; the similar ones are perceived as parts of the same object whereas different ones are distinguished.
• Principle of closure describes our tendency to perceive overlapping pierced or half forms as complete ones, and ignore the gaps in the borders.
• The principle of good continuation involves the grouping of intersecting lines as single, smoother, longer ones rather than disconnected or sharply bent ones.
• Principle of common movement describes the tendency to perceive singular elements moving at the same speed to the same direction as parts of a whole larger element.
• Principle of good form describes our tendency to perceive rather symmetric objects as singular ones whereas asymmetric forms as overlapping or conjoined more simple shapes.
• All these principles help distinguish, integrate, analyse, follow and derive meaning from forms and shapes we see to create meaningful images in our heads.

Question 16

FQ.16: How do reversible figures illustrate the visual system’s strong tendency to separate figure and ground, even in the absence of sufficient cues for deciding which is which?

Answer 16

• Reversible figures indicate our tendency to derive rather comprehensible figures from unusual elements we are presented with, as an act of decision to perceive one object or the other depending on present cues even if they aren’t sufficient.
• Our perception oscillates between the alternatives – perceiving one element as the main figure and the other as the background and vice versa – to derive a meaning from what we are seeing.

Question 17

FQ.17: How do illusory contours illustrate the idea that the whole influences the perception of parts? How are illusory contours explained in terms of unconscious inference?

Answer 17

• Illusory contours are actions of our brain done to infer meaning from an unusual setting of elements, which alters our perception of the parts as well.
• Unconscious inference is the process that brain uses to assess meaning and presence of a possible element amongst a uniquely and unusually arranged set of elements.

Question 18

FQ.18: How is unconscious inference described as top-down control within the brain? What is the difference between top-down and bottom-up control?

Answer 18

• When responsible neurons in a higher brain area are stimulated with an input, they infer meaning from the feedback and command downwards their conclusion, which is top-down control.
• Unconscious inference occurs as visual input activates relevant neurons.
• Bottom-up control is stimulation of the neurons directly by the sensory input and not higher parts of the brain as it is in top-down control.

Question 19

FQ.19: How does the existence of two types of visual deficits caused by brain damage provide support for the idea that the human brain does indeed process objects as distinct entities?

Answer 19

• Visual object agnosia patients can describe separate elements of the object in great depth, but they cannot identify the object as a whole relying only on sight.
• Visual form agnosia patients cannot see the outlining and patterns of a presented object even though being aware of the object’s presence and able to perceive some of its features such as colour and brightness. They can reach out to grab it or move around it easily.
• These deficits are caused by damage to separate brain portions and impair different abilities of visual perception which indicates that our perception of objects is made up of separate elemental entities conjoined to derive a meaning.

Question 20

FQ.20: What are the anatomical and functional distinctions between two different visual pathways in the cerebral cortex?

Answer 20

• One of the pathways is the “what” pathway, or the lower stream running into the temporal lobe, is responsible for identifying the objects themselves.
• The other is the “where” or “where-and-how” pathway, or the upper stream running into the parietal lobe, is responsible for spatial localisation of the objects and arrangement of actions to properly interact – or avoid – said objects.

Question 21

FQ.21: What abilities are preserved in people with damage to the “what” pathway but lost in people with damage to the “where-and-how” pathway?

Answer 21

Damage to the where-and-how pathway does not affect one’s ability to perceive and identify objects as is the case in “what” pathway, however it impairs one’s ability to properly locate and interact or avoid an object in space.

Question 22

FQ.22: In sum, what are the distinct functions of the “what” and “where-and-how” visual pathways?

Answer 22

The “what” pathways allows us integrate various elements of an object into a complex, whole vision of it as well as create memories, plans and consciously identify it; the “where-and-how” pathways allows us to create and unconscious map of the space surrounding us and properly locate and interact with objects around us, such as moving around obstacles, reaching for and grasping objects etc.

Question 23

FQ.23: What evidence is there that people use different psychological mechanisms to recognize faces than they use to recognise nonface objects?

Answer 23

Unlike everyday objects, we seem to pay special attention to faces, remember, recognise and distinguish thousands of them. We apparently use different, specialised brain areas to do so. Some distinct features and elements of a face give us an immediate perception of a face, and we can even infer faces from non face objects.

Question 24

FQ.24: How does the own-race bias and its development support the idea that learning is involved in recognizing faces?

Answer 24

Studies conducted with babies of different races and different ages indicate that own-race bias is in fact developmental, since 3 month old babies were able to distinguish between faces of every race when given the chance to observe; and these scores kept getting lower for other races in older babies.

Question 25

FQ.25: How did Helmholtz describe perception as a problem-solving process?

Answer 25

According to Helmholtz, the light reaching us is not the vision itself. The brain processes the visual cues reaching us to infer a complete image of our surroundings without our awareness.

Question 26

FQ.26: How does binocular disparity serve as a cue for depth?

Answer 26

Binocular disparity is the difference of angle from which our eyes perceive vision. This allows us to assess the degree of parallelism between visual cues from an object, and perceive its depth according to the amount of binocular disparity; the more parallel is the visual input, the further away the object is.

Question 27

FQ.27: How do stereoscopes provide an illusion of depth?

Answer 27

A stereoscope provides two pictures of a setting from slightly different angles, to simulate the binocular disparity of our eyes. When these images merge in our eyes, our brain recognises the fusion of the same image with different angles and the depth effect is created.

Question 28

FQ.28: How does motion parallax serve as a cue for depth, and how is it similar to binocular disparity?

Answer 28

Motion parallax is the perception of depth of an object with respect to its background, caused by head movements. Even with one eye, this can be perceived. It is simply the change in the angle from which an object is viewed and its measure of severity with regard to the head movement. The less the object moves, the further away it is. It is similar to binocular disparity as both rely on differences in angle.

Question 29

FQ.29: What are some cues for depth that exist in pictures as well as in the actual, three-dimensional world?

Answer 29

• occlusion, the cue in which some objects obstruct other’s parts and seem to be closer to the viewer than the cut image;
• relative image size for familiar objects, the cue that helps us assess a distance to each object depending on our knowledge about their size and how they should appear in which distance;
• linear perspective, the cue in which rows of objects or linear objects converge as they go further away from which we perceive distance;
• texture gradient, the cue in which the accumulation of objects or texture features spread out when they are closer and accumulate as they are further away;
• position relative to the horizon, the cue in which we assess an object’s distance with regard to its apparent distance to the horizon;
• differential lighting of surfaces, the cue in which we assess distance to objects with regard to their lighting.

Question 30

FQ.30: Why does size perception depend on distance perception?

Answer 30

The size of the image of an object created in the retina is inversely proportional to its distance. Therefore the further away the object is, the smaller the retinal image gets. If an object is perceived as further away, this smaller image will not impact the perceived size of the object.

Question 31

FQ.31: How might the unconscious assessment of depth provide a basis for the Ponzo, Müller-Lyer, and moon illusions?

Answer 31

This assessment bases our illusory perceptions on our instinct to assess distance to the visuals we see, which in turn, even if falsely, gives us the perception that if one of the objects appears farther away and they appear to be the same size, the farther one must be larger than the other.

Question 32

FQ.32: What is the McGurk effect and how does it demonstrate visual dominance?

Answer 32

McGurk effect is a demonstration of our tendency to rely on visual cues more than auditory ones and to trust vision when two senses conflict. It is basically a sound (ba) accompanied by a vision of a mouth move (ga). If the movement and the sound match, we’ll easily perceive it; but if they are different, we’ll either try to derive the sound not from the sound itself but from the mouth movement, or we’ll perceive a completely different sound altogether.

Question 33

FQ.33: What are the defining features of synesthesia? Might synesthesia have any adaptive value?

Answer 33

Synesthesia has to be involuntary, automatic, consistent, spatially extended, memorable and emotional. Synesthesia apparently contributes to the perception of high-order concepts and unusual metaphors as well as artistic creation.