Perception

Question 1

What are the 5 steps in perception?

Answer 1

stimulus, transduction, sensation, perception, recognition

Question 2

What are the different types of stimulus?

Answer 2

Distal stimulus: the source of the change in your organism e.g. the light.
Proximal stimulus: changes in retina for example. The change occurs directly in the body.

Question 3

What is sensory modality and give examples?

Answer 3

sensory modality, is one aspect of a stimulus or what is perceived after a stimulus.

For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation.

Question 4

What are the characteristics of sensory receptors?

Answer 4

Range: each sensory modality responds to a limited range of stimuli.
Adaptation: for the eyes, there is a depletion of chemicals, e.g. (machband effect?). Adjustment of the sensory system’s sensitivity to the current environment (e.g. when it goes dark your eyes adapt).
Acuity: how well we can distinguish among stimuli within a sensory modality. The smallest difference in color you can perceive.

Question 5

Describe vision as a sensory modality.

Answer 5

Retina: cones for colors. Rods for night vision but not detailed. There is a blind spot in the eye.

Relative encoding: so what matters is contrast. Absolute encoding would limit us in how many colors we can perceive.

Question 6

Describe auditory and vestibular modalities

Answer 6

Auditory: air vibration and waves of pressure change, vibrations magnified in the cochlea.
Vestibular system: balance and movement.

All sensory information (except olfactory which goes directly to the brain) passes through the thalamus and goes to the different parts of the brain to be further processed.

Question 7

What is transduction?

Answer 7

Transduction (peripheral processing): transformation of one type of energy e.g. light, into another electric energy in the brain. Ion channels are closed if there is PSP.

Question 8

What is the difference between sensation and perception?

Answer 8

Sensation: bottom-up activation of our sensory system by a stimulus. Occurs when sensory organs absorb energy from a physical stimulus, the sensory receptors transform into electric signals that go into the brain.

Perception: it reflects the idea that you recognize what you are sensing.

Question 9

Describe the difference between structuralism and gelstalt.

Answer 9

Structuralism: adding up sensations.
Gestalt: the whole differs from the sum of its parts. Not just the sum of its sensations. It is not just adding single features…

Question 10

What is the sensation vs perception debate?

Answer 10

Sensation vs perception debate: apparent motion from one rectangle to another but it is really just two rectangles flashing. The blue circles which are moving.

You can manipulate the movement of the red dot (look at the paper). Example of the triangle and cube, also the arrow/lines with the illusion of one being longer than the other. So discrepancy of what the retina senses and what your brain perceives! So perception is an inference. Example with blurry images where the sensation is noisy but if the context is generous then we can perceive. The blob example.

Question 11

What is the theory of unconciuous inferences?

Answer 11

Perception is the result of unconscious assumptions.
Likelihood principle: we perceive the object that is most likely (past experiences) to have caused the pattern of the stimuli we receive.

When you are a baby, all the sensations are noise, neurons are less activated. But as you grow you get statistical regularities and networks that will be used over and over again as an adult. Example of the rectangles.

Question 12

Describe perception as a result of bayesian inference/theory.

Answer 12

Perceiving is inferring from the 2D image created in the retina (proximal stimulus) what caused it (distal stimulus) in a 3D environment → inverse problem in the sense of Bayesian statistics using prior belief and posterior and likelihood.

Info sent by proximal stimulus so perception is the best hypothesis to make sense of what you sense.
Posterior beliefs are a combination of evidence and prior beliefs. Depends on the number of parameters for the crossed line example (two intersecting lines or two acute angles, so you have two models to compare). Same example for the image of the duck that also looks like a rabbit at the same time.

Perception is model comparison. Parsimony is key to the model comparison. You want a representation of the world where you can make predictions of what will happen in the world.

Question 13

What is perceptual constancy?

Answer 13

Perceptual constancy: tendency to see objects as having standard shape, size, color or location regardless of changes in the angle, perspective, distance or lighting (proximal changes). Responsible for the ability to identify objects under various conditions.

Question 14

Example of perception not equal to sensation

Answer 14

What we perceive is not what we see. Ames’ room. Size and color constancy.
The dress: warm vs cool illumination.
We perceive colors as they should be given the environment, we do not perceive colors that are actually entering the eye.

Question 15

What is object recognition?

Answer 15

Object recognition: matching what you sense with something you have in memory. Noise with dog example.

Question 16

What are some diseases that impact object recognition?

Answer 16

Visual agnosias: incapacity to recognize subjects.
Prosopagnosia: incapacity to recognize faces.

Question 17

Which are the visual pathways in the brain?

Answer 17

Two visual pathways: the what which is in the temporal lobe. The where in the parietal lobe. Fusiform face area for face recognition.

Question 18

What is the direct approach of object recognition?

Answer 18

Direct approach: sense of objects comes from their affordance (possible uses, what they are built for). No mental representations needed. Stimuli carry enough information to be correctly perceived and identified. Importance of bottom-up approach. The basic process of object perception and recognition is a process of resonance (receiver analogy)

Question 19

What is size constancy?

Answer 19

Size constancy refers to the fact that our peceptions of the size of objects are relatively constant despite the fact that the size of objects on the retina vary greatly with distance

Assuming size constancy, our visual system estimates the size of any object as follows : retinal distance size multiplied by the assumed distance. Monster example: we think one monster is bigger than the other based on contextual cues such as perpective, but actually they are the same size

Question 20

What is color constancy?

Answer 20

Color constancy refers to our ability to perceive colors as relatively constant over varying illuminations (i.e. light sources). For example, a red apple will still look red on a sunny day or cloudy day – or in a grocery store or a home.

Question 21

What is the indirect approach in object recognition?

Answer 21

Importance of top-down processes:we perceive and interpret the stimuli in the light of our beliefs, knowledge or expectations
* 4 postulates on object recognition process
–Active process(not only stimuli driven)
–Does not directly come from stimulus(hypothesis driven)
–Influenced by motivation
–Our desires or beliefs can lead to illusions

Question 22

What is perception based on according to Gestalt?

Answer 22

Principle of proximity : proximal elements in the visual field tend to be grouped
Principle of similarity : similar elements tend to be perceived together
Principle of continuity: we are grouping the elements that need less changed or interruption
Principle of closure: we fill the empty elements

Question 23

What is representational momentum?

Answer 23

Representational momentum is a small, but reliable, error in our visual perception of moving objects. Instead of knowing the exact location of a moving object, viewers actually think it is a bit further along its trajectory as time goes forward.

For example, people viewing an object moving from left to right that suddenly disappears will report they saw it a bit further to the right than where it actually vanished.

The perceived offset point is always shifted from the true location in the direction of movement → Anticipated motion

Question 24

What is object recognition by template matching?

Answer 24

It is a theory that assumes every perceived object is stored as a “template” into long-term memory.[4] Incoming information is compared to these templates to find an exact match. In other words, all sensory input is compared to multiple representations of an object to form one single conceptual understanding.

The theory defines perception as a fundamentally recognition-based process. It assumes that everything we see, we understand only through past exposure, which then informs our future perception of the external world.For example, A, A, and A are all recognized as the letter A, but not B.

Question 25

What is Marr’s theory of vision?

Answer 25

Marr attempted to set out a computational theory for vision as a whole. He suggested that visual processing passes through a series of stages, each corresponding to a different representation, from retinal image to ‘3D model’ representation of objects.

Question 26

What is the recognition by component theory?

Answer 26

We are able to recognize objects by separating them into geons(the object’s main component parts). *Geons are based on basic 3-dimensional shapes (cylinders,cones,etc.)

Steps:
1- segmentation of visual field: extraction of borders of object and concave shapes
2- geon recognition: identify invariant properties of objects such as symmetry, angles, etc.
3- matching to what is stored in memory.

Question 27

What is the absolute threshold in measuring perception?

Answer 27

An absolute threshold is the smallest amount of stimulation needed for a person to detect that stimulus 50% of the time.

Why not 100%? That is because our absolute threshold can vary according to external and internal factors like background noise, expectation, motivation and physical condition.

The affirmation that there is no single absolute threshold is called signal detection theory. Because our perception responses may vary, to find a person’s absolute threshold researchers conduct multiple tests until they find the amount that is perceived 50% of the time.

There is also another factor that influences the absolute threshold: sensory adaptation. Sensory adaptation happens when a stimulus remains the same for a long period of time, and our bodies stop recognizing it.

Question 28

What is the difference threshold?

Answer 28

A difference threshold is the minimum required difference between two stimuli for a person to notice change 50% of the time. The difference threshold is also called just noticeable difference.

Example: The smallest difference in sound for us to perceive a change in the radio’s volume

Question 29

What is weber’s law?

Answer 29

Weber’s Law states that rather than a constant, absolute amount of change, there must be a constant percentage change for two stimuli to be perceived as different. In other words, the higher the intensity of a stimulus, the more it will need to change so we can notice a difference.

Example: You can notice a difference when you go from volume 1 from volume 3, for example, but you don’t perceive the same difference when the volume goes from 40 to 43. According to Weber’s Law, for you to perceive the difference between volume 40 and 43 the same way you perceived the difference between volume 1 and 3 (an increase of 300%), volume 40 would have to go up to 120 (the same increase of 300%).

Question 30

Magnitude estimation for sensory stimuli

Answer 30

Assigning a value to the intensity of a light (for example), and then showing different changes to light intensity and then ask participants how much did it change…

Response compression : As intensity increases, the perceived magnitude increases more slowly than the intensity –> example: brightness
Response expansion : As intensity increases, the perceived magnitude increases more quickly than the intensity –> electric shock

neutral example without response compression/expansion: line length.