Lesson 1: Sensation

Question 1

How would your perception change if you only had one eye?

Answer 1

You wouldn’t be able to use binocular cues such as convergence or retinal disparity. This would make you less able to accurately perceive depth.

Question 2

The fact that a human’s eyes are about 2.5” apart allow humans to get slightly different views of objects from each eye and thus results in a perception of depth. Which binocular cue does this describe?

(A) Interposition
(B) Convergence
(C) Constancy
(D) Retinal Disparity

Answer 2

(D) Retinal disparity

Retinal disparity refers to the fact that the eyes are about 2.5” apart. This binocular cue allows humans to get slightly different views of objects from each eye, which enables a perception of depth.

Question 3

True or False? Constancy is a perceptual category in which our perception of an object remains the same even if the image cast on the retina is different.

Answer 3

True. Constancy is a perceptual category in which our perception of an object remains the same even if the image cast on the retina is different.

Question 4

What does shape constancy refer to? Can you give an example?

Answer 4

Shape constancy is the tendency to perceive an object as the same shape even as the object projects a different shape to our retina.

Ex) As the quarter changes in position, its shape can change from a circle to a rectangle, however, no matter what its shape looks like, we always associate the quarter to a circle.

Question 5

CRB Sensation and perception are often used interchangeably in daily life, but have different scientific definitions. Which of the following statements is NOT true?

(A) Sensation is more closely related to transduction.
(B) Perception is more closely related to processing information.
(C) Sensation and perception occur simultaneously and instantly.
(D) Sensation relies upon receptors, whereas perception relies upon the central nervous system.

Answer 5

(C) Sensation and Perception occur simultaneously and instantly.

Sensation must occur before Perception, because the stimuli must be transduced and sent to the central nervous system before it can be perceived.

Question 6

Sensory adaptation can protect your ears (via the tympanic reflex) from damage during a long fireworks display. How does this work?

Answer 6

The inner ear muscle contracts after an increased, sustained stimulus, decreasing ossicle vibration and downstream sensitivity.

Question 7

The following senses are subject to sensory adaptation. Describe how this occurs for each.

• Hearing
• Touch
• Smell
• Propioception
• Sight

Answer 7

Hearing - Tympanic reflex: inner ear muscle contracts to really loud noises.
Touch - After being in cold water for a long time, nerves stop firing.
Smell - Can be desensitized to perfume over time.
Propioception - Can adjust to a different position of the body in space.
Sight - Pupil dilation/constriction is used to adjust to different intensities of light.

Question 8

CRB Fill in the blanks: Sensory receptors can be separated by the origin of their stimuli; receptors that detect the outside world are __________ and receptors that detect internal stimuli are _______.

(A) Mechanoreceptors, Nociceptors
(B) Nociceptors, Mechanoreceptors
(C) Exteroreceptors, Interoreceptors
(D) Interoreceptors, Exteroreceptors

Answer 8

(C) Exteroreceptors, Interoreceptors

Sensory receptors can be separated by the origin of their stimuli; receptors that detect the outside world are exteroreceptors and receptors that detect internal stimuli are interoreceptors.

Question 9

CRB _________ stimuli directly interact with and affect sensory receptors and are used to interpret the _________ stimuli, which are the “actual” objects in the environment.

(A) Distal, Proximal
(B) Proximal, Distal
(C) Lateral, Medial
(D) Medial, Lateral

Answer 9

(B) Proximal, Distal

Proximal stimuli directly interact with and affect sensory receptors and are used to interpret the distal stimuli, which are the “actual” objects in the environment.

Question 10

How can sight be both down- and up-regulated in terms of pupil and cone/rod adjustment?

Answer 10

Down-regulated: when it’s very bright outside the pupil constricts, and the cones & rods desensitize to light

Up-regulated: when in a dark setting the pupils dilate, and cones & rods synthesize light-sensitive molecules

Question 11

You look at a group of lightbulbs and notice that some are brighter than others. You are unable to tell however that two of the lightbulbs have a difference in intensity, seeming to be the same brightness. How does the concept of just-noticeable difference (JND) apply in this context?

Answer 11

When you are able to perceive a difference in brightness, the difference in intensity of light has surpassed your JND. When you are not able to perceive a difference, it has not.

Question 12

What is the purpose of Weber’s Law?

Answer 12

To quantify the just-noticeable difference (JND) of tactile and auditory sensations.

Question 13

What is the equation for Weber’s Law?

Answer 13

ΔI/I = K

I = Background Intensity
K = Weber's Fraction
ΔI = Incremental Threshold

Question 14

You are at a rock concert and the music is playing at an intensity of 70 watts. The rock band members turn up the volume just enough that you notice a difference in sound level intensity. If Weber’s fraction is equal to .1 in this case, what is the JND?

(A) .1 W
(B) 7 W
(C) 10 W
(D) 70 W

Answer 14

(B) 7 W

ΔI/I = K
ΔI/70 W = 0.1
ΔI = 7 W

Question 15

A child is taking a hearing test. How might the concept of absolute threshold of sensation apply to this situation?

Answer 15

The absolute threshold of sensation is a generally detectable stimulus. It is defined as the minimum intensity of a stimulus needed to detect that stimulus at least 50% of the time. Thus, for a child taking a hearing test, it would be the point at which the child begins to detect the sound in their ear at least 50 percent of the time.

Question 16

What is the difference between the difference threshold (JND) and the absolute threshold of sensation?

Answer 16

The difference threshold is the smallest difference BETWEEN STIMULI that can be detected 50% of the time.

The absolute threshold is the minimum intensity of A STIMULUS that is needed to detect a particular stimulus 50% of the time.

Question 17

How might the following external factors influence the absolute threshold of how likely an individual is to notice that their spouse is speaking to them while they are studying for the MCAT?

• Expectations of stimuli
• Experience
• Motivation
• Alertness

Answer 17

Expectations of stimuli - If you expect your spouse to speak to you while you are studying, you will be more likely to notice when it happens.
Experience - If your spouse speaking to you is a common experience, you may be more likely to recognize it.
Motivation - If you are motivated to impress your spouse, you may be more likely to pay attention.
Alertness - If you are less tired while studying, you will be more likely to perceive that your spouse is speaking to you.

Question 18

Homer Simpson walks into a cult meeting. He doesn’t even notice the strange symbols on the wall and the fact that everyone is dressed strangely. How might this relate to the concept of subliminal stimulus?

Answer 18

The subliminal stimulus is a stimulus that is below the absolute threshold of sensation (less than 50% detected/not detected by an individual). The symbols and clothing must be below Homer’s absolute threshold, and are examples of subliminal stimuli.

Question 19

CRB True or false? Thresholds can also be called limina, which is the root of “subliminal”

Answer 19

True. Thresholds can also be called limina, which is the root of “subliminal”.

Question 20

What cues does the body perceive and receive from the different types of somatosensations in order to process information?

I. Intensity
II. Timing
III. Location

(A) I only
(B) I and II
(C) II and III
(D) I, II, and III

Answer 20

(D) I, II, and III

The body receives information from the different types of somatosensations by intensity (how quickly the neurons in our body fire), timing (the timing of the neurons firing), and the location (where the neurons are firing).

Question 21

CRB True or false? The central nervous system is able to determine the modality of a stimulus (the type of stimulus) based on the length traveled by the signal.

Answer 21

False. The central nervous system is able to determine the modality of a stimulus (where it came from) based on which RECEPTOR TYPE is firing.

Question 22

What is detected by the 4 Types of Somatosensation?

• Thermoception
• Mechanoception
• Nociception
• Propioception

Answer 22

Thermoception (temperature)
Mechanoception (pressure)
Nociception (pain)
Propioception (position)

Question 23

Sally is touching a hot stove. She thinks that the action potential that sent the signal to her brain must be really big and strong. How would you respond to Sally’s reasoning?

Answer 23

Tell her that action potentials are always the same size, but that the intensity of her pain is encoded via the frequency with which nerve cells fire. It’s not that the action potential is really big, but that many action potentials are being sent to her brain in a very short period of time.

Question 24

There are three ways for a neuron to encode timing (when a stimulus starts and stops). Describe each:

• Non-adaptive
• Slow-adapting
• Fast-adapting

Answer 24

Non-adaptive: neuron firing rate will not change over time, and is fired at a constant rate.
Slow-adapting: slowly will adapt to stimulus over time (action potentials start fast but become less and less frequent until they finally stop altogether).
Fast-adapting: will fire quickly at the beginning, then stop, and fires again once stimulus stops.

Question 25

How is location of a stimulus encoded by a dermatome?

Answer 25

Each dermatome corresponds to an area of skin supplied by mainly one spinal nerve. Whichever dermatome is firing indicates the position.

Question 26

What is the purpose of the anterior, posterior and lateral/horizontal canals (aka semicircular canals)? By what mechanism do they work?

Answer 26

All 3 canals are orthogonal (90°) to each other and contain endolymph. As we rotate, the endolymph moves in these canals, and is key in helping the vestibular system know both how one is rotated in space, and the strength of that particular rotation.

Question 27

What is the purpose of the otolithic organs (utrical and saccule)?

Answer 27

These help determine acceleration and head positioning. They have calcium carbonate crystals that are attached to hair cells, and depending on our head positioning, these crystals pull on the hair cells which causes an action potential, which ultimately leads to the detection of acceleration and positioning.

Question 28

Signal detection theory helps us make decisions in situations of:

I. Certainty
II. Uncertainty
III. Audition

(A) I Only
(B) II Only
(C) I and II Only
(D) I, II, and III

Answer 28

(B) II Only

Signal detection theory helps us with “decision making with uncertainty”. It answers the question of “at what point is a signal strong enough to notice?”

Question 29

On a very foggy day, a driver can have trouble seeing the traffic light. How could this be an example of signal detection theory?

Answer 29

With thick fog, the driver will guess when the light is green (a decision made with uncertainty).

Question 30

Which signal detection strategies correspond with a C > 0, and C < 0?

Answer 30

Conservative –> (C > 0)

Liberal –> (C < 0)

Note that this is different than what is written inside the video, but on the Khan Academy website they acknowledge the error in the comments.

Question 31

When graphing signal detection theory, D represents the distance between the peaks of the noise curve and the signal curve. As D decreases, what happens to the frequency of misses/false alarms?

Answer 31

As the distance ,D, decreases, the more common misses and false alarms will be.

Question 32

Compare bottom-up vs. top-down processing.

Answer 32

Bottom-up processing occurs when stimuli influence our perception. It is a data driven process in which no preconceived knowledge is utilized. It is a slow process.

Top-down processing occurs when background knowledge influences our perception. It is a theory-driven process. It is quicker but more prone to mistakes.

Question 33

When traveling to the Eiffel Tower for the first time, tourists may still get a feeling of deja-vu. Why is this the case in terms of bottom-up and top-down processing?

Answer 33

Tourists have probably seen pictures of the Eiffel Tower, so top-down processing will quickly recognize the structure before bottom-up processing can actually process the stimuli.

Question 34

What is the purpose of the Gestalt principles? What phenomena do they explain?

Answer 34

Gestalt principles are a set of principles that explain how humans naturally perceive stimuli in the most simple and organized manner possible.

Question 35

Draw or visualize an example of the law of Prägnanz. Describe this law.

Answer 35

Reality is reduced to its simplest form.

Law of Pragnanz: Reality is organized or reduced to the simplest form possible (example the Olympic symbols)

Question 36

Draw or visualize an example of the law of proximity. Describe this law.

Answer 36

Objects close in space are grouped together.

Law of proximity: Objects near each other tend to be grouped together

Question 37

Draw or visualize an example of the law of continuity. Describe this law.

Answer 37

Lines are seen as following the smoothest path.

Continuity: Objects that appear to form a pattern are perceived as units

Question 38

Draw or visualize an example of the law of closure. Describe this law.

Answer 38

Objects grouped together are seen as a whole, and any gaps that may appear are ignored.
Law of Closure: we tend to ignore gaps and complete contour lines

Question 39

As John looks at a tree in the distance, his eyes are relaxed. However, when he begins to look at a pencil on the desk in front of him, his eyes must turn towards the pencil. The relaxing and turning of John’s eye muscles allow John to have sense of depth. Which binocular cue does this refer to?

(A) Motion Parallax
(B) Shading and Contour
(C) Convergence
(D) Retinal Disparity

Answer 39

(C) Convergence

Convergence is a binocular cue that enables depth perception, and which is based on how relaxed and turned a human’s eyeballs are. When an object is far away our eye muscles are relaxed, and when an object is close, the eye muscles turn our eyes toward the object.

Question 40

While driving, Adam missed his street because that sign was blocked by a closer stop sign. Which monocular cue is this most like? Explain.

(A) Relative size
(B) Interposition
(C) Relative height
(D) Shading and contour

Answer 40

(B) Interposition

Interposition allows humans to infer that an object that is directly in front of another object is closer to us than the other object.

Question 41

You see two motorcycles. One looks smaller than the other and you assume that it must be further away in the distance. What monocular cue is likely responsible for this? Explain.

(A) Relative size
(B) Interposition
(C) Relative height
(D) Shading and contour

Answer 41

(A) Relative size

Relative size tells us objects that are smaller are perceived as being further away.

Question 42

The Cornsweet Illusion has two blocks stacked on top of each other, apparently at an angle. Each block is the same shade of gray, but one appears darker. Which monocular cue is causing this? Explain.

(A) Motion Parallax
(B) Interposition
(C) Relative height
(D) Shading and contour

Answer 42

(D) Shading and contour

Shading and contour tells us that the central edge has a large contrast of colors; the outer regions of each block are perceived as more similar to their side of the central edge than the other block’s outer region, even though those 2 blocks’ outer regions are the same hue.

Question 43

You see two trees ahead of you. One is higher than the other and is perceived to be further in the distance. Which monocular cue is responsible for this? Explain.

(A) Motion Parallax
(B) Interposition
(C) Relative height
(D) Shading and contour

Answer 43

(C) Relative height

Relative height is a cue that tells us that objects that are higher in our visual field are perceived to be further away.

Question 44

Driving through the Appalachians, the nearby traffic signs appear to be moving faster than the further mountain peaks. Which monocular motion cue is causing this? Explain.

(A) Motion Parallax
(B) Interposition
(C) Relative height
(D) Shading and contour

Answer 44

(A) Motion Parallax

Motion parallax is a cue which tells you that closer objects seem to move quicker than further objects as we move (relative motion).

Question 45

What type of constancy refers to the fact that even though an image may look bigger than another image because it is closer, we still process the images as the same size?

(A) Size Constancy
(B) Shape Constancy
(C) Relative Constancy
(D) Color Constancy

Answer 45

(A) Size Constancy

Size constancy describes the fact that even though an image may look bigger than another image because it is closer, we still process the images as the same size.

Question 46

What type of constancy refers to the color of an object remaining the same to our perception despite changes in illumination?

(A) Size Constancy
(B) Shape Constancy
(C) Relative Constancy
(D) Color Constancy

Answer 46

(D) Color Constancy

Color constancy; Bananas are still perceived as yellow despite different shading.

Question 47

What does sensory adaptation refer to? Can you give an example?

Answer 47

Sensory adaptation is described as a change in the sensitivity of one’s perception of a sensation and allows humans to adapt to their surroundings.

Question 48

Based on Weber’s law, as the background intensity (I) increases, the incremental threshold (ΔI) increases as well. What type of relationship does this represent?
(Weber’s Law: ΔI/I = K)

(A) Exponential
(B) Hyperbolic
(C) Linear
(D) Sigmoidal

Answer 48

(C) Linear

For example, in a quiet room with low background intensity (I) the incremental threshold (ΔI) is small, however at a loud concert the background intensity is much greater, and thus the incremental threshold is much greater as well.

Question 49

When you first jump into a very cold pool, you will noticeably feel the cold. After a while, however, you stop feeling cold. What type of neuron timing does this represent?

(A) Non-adaptive
(B) Slow-adapting
(C) Fast-adapting
(D) Light-adapting

Answer 49

(B) Slow-adapting

The cold is sensed for a considerable amount of time before stopping. Meaning that slow-adapting neuron timing is involved here.

Question 50

There are 4 possible outcomes of signal detection:

(1) Hit
(2) False Alarm
(3) Miss
(4) Correct rejection

Describe each of these in terms of a signal being present or not, and whether or not that signal was detected.

Answer 50

Signal
Present Absent

Response Yes HIT FALSE
ALARM
No MISS CORRECT
REJECTION

Question 51

CRB In a signal detection theory experiment, a subject was only getting hits on 45% of the catch trials (trials with a signal present). What does this say about the signal’s absolute threshold?

(A) The signal is below absolute threshold, because it was not being recognized at least 50% of the time.
(B) The signal is below absolute threshold, because it was not being recognized in each and every trial (100%).
(C) The signal is above absolute threshold, because it is being detected correctly sometimes (> 0%).
(D) There is no relationship between signal detection theory experiments and absolute threshold.

Answer 51

(A) The signal is below absolute threshold, because it was not being recognized at least 50% of the time.

Question 52

Which two signal detection variables denote the strength of a signal and the strategy to determining a signal?

(A) d’ and c
(B) B and d’
(C) c and B
(D) B and B

Answer 52

(A) d’ and c

d’ - Strength of a signal. Says how often you will hit compared to a miss.
c - Strategy. Determines what x-value is significant enough to cause action.

Question 53

A _________ signal detection strategy will correctly reject any time there is no signal, however may miss a signal when present. A ________ signal detection strategy will always correctly choose a hit, but will also detect false alarms.
Which answer choice correctly fills in the blank?

(A) Liberal, Conservative
(B) Conservative, Liberal
(C) Liberal, Non-liberal
(D) Conservative, Non-liberal

Answer 53

(B) Conservative, Liberal

A conservative signal detection strategy will correctly reject any time there is no signal, however may miss a signal when present.

A liberal signal detection strategy will always correctly choose a hit, but will also detect false alarms.

Question 54

Match the type of reasoning with the type of processing:

(A) Inductive Reasoning
(B) Deductive Reasoning

(1) Bottom-up processing
(2) Top-down processing

Answer 54

(A) Inductive Reasoning -> (1) Bottom-up processing
(B) Deductive Reasoning -> (2) Top-down processing

Inductive reasoning moves from a specific instance to a generalized conclusion, just like bottom-up processing.

Deductive reasoning moves from generalized principles to a specific conclusion, similar to top-down processing.

Question 55

Draw or visualize an example of the law of similarity. Describe this law.

Answer 55

Similar items are grouped together by the brain.