Sensation and perception sample question 1

Rapidly adapting receptors, which respond to changes such as vibration

Sensation and perception sample question 2

Attention was directed to the counting task, so an unexpected stimulus fell on the retina but did not reach awareness.

Sensation and perception sample question 3

adopted a more conservative response criterion.

Sensation and perception sample question 4

Observer Q is more sensitive, because Q's Weber fraction (12/300 = 0.04) is smaller than P's (3/50 = 0.06)

Sensation and perception sample question 5

Above the brainstem each ear reaches both hemispheres, so one cortex still hears both ears, but the right cortex favours the left side of space.

MCAT · Psychological, Social, and Biological Foundations of Behavior · Psychology

Sensation and perception

Sensation and perception is part of Psychology in the MCAT Psychological, Social, and Biological Foundations of Behavior section. The questions below are written in the style of the real test, each with the answer and a worked explanation.

Question types you will see here include signal detection: criterion versus sensitivity, weber fraction prediction, top-down versus bottom-up processing and sensory adaptation versus habituation.

Common traps: reading a shift in overall yes-responses as better sensitivity; counting false alarms as misses; assuming a payoff change alters sensitivity rather than the criterion.

Sample questions

Question 1
A student feels her phone buzz in her pocket, but within a minute no longer feels the steady pressure of the phone's weight. Which receptor type best explains the buzzing sensation?
- A.
  Slowly adapting receptors, which respond throughout sustained pressure
- B.
  Rapidly adapting receptors, which respond to changes such as vibration
- C.
  Thermoreceptors, which respond to changes in temperature
- D.
  Nociceptors, which respond to damaging stimuli
Answer: B. Rapidly adapting receptors, which respond to changes such as vibration
B is correct: rapidly adapting receptors (Pacinian type) fire for changing stimuli such as a buzz and fall silent to constant pressure. A would keep firing to the steady weight, C signal temperature, and D signal potentially damaging stimuli, none of which the buzz is.
Question 2
Viewers asked to count basketball passes between players in white shirts often fail to notice a person in a gorilla suit who walks through the scene for several seconds. Which explanation is best?
- A.
  The retina could not detect the dark costume, which lay below the absolute threshold.
- B.
  Sensory adaptation to the continuous motion in the scene reduced responses to it.
- C.
  Attention was directed to the counting task, so an unexpected stimulus fell on the retina but did not reach awareness.
- D.
  A cut between two versions of the scene concealed the change.
Answer: C. Attention was directed to the counting task, so an unexpected stimulus fell on the retina but did not reach awareness.
This is inattentional blindness: focused attention on one task limits awareness of an unexpected object that the eye still receives, C. A wrongly blames the sensory threshold; B confuses it with adaptation to constant input; D describes change blindness, which needs an interruption.
Question 3
A radiologist learns that a particular type of tumor is far rarer than she had believed. Afterward, she reports fewer tumors both on scans that contain them and on scans that do not, while her ability to distinguish the two types of scans is unchanged. In signal detection terms, she has:
- A.
  increased her sensitivity (d').
- B.
  adopted a more liberal response criterion.
- C.
  adopted a more conservative response criterion.
- D.
  lowered her absolute threshold for detecting tumors.
Answer: C. adopted a more conservative response criterion.
Fewer hits and fewer false alarms together, with no change in discriminability, indicate a more conservative criterion: she now requires more evidence before reporting a tumor. A more liberal criterion would increase both hits and false alarms, and sensitivity is stated to be unchanged.
Question 4
Observer P can just detect a 3 g difference when holding 50 g, and observer Q can just detect a 12 g difference when holding 300 g. Which statement is correct if Weber's law holds for both?
- A.
  Observer Q is more sensitive, because Q's Weber fraction (12/300 = 0.04) is smaller than P's (3/50 = 0.06)
- B.
  Observer P is more sensitive, because P's just noticeable difference of 3 g is smaller
- C.
  Observer P is more sensitive, because P's Weber fraction of 0.06 is larger than Q's
- D.
  The observers are equally sensitive, because Weber's law states that the just noticeable difference is the same for all baselines
Answer: A. Observer Q is more sensitive, because Q's Weber fraction (12/300 = 0.04) is smaller than P's (3/50 = 0.06)
Sensitivity is compared with the Weber fraction, the JND divided by baseline: Q 0.04 and P 0.06, so a smaller fraction means higher sensitivity (A). B compares absolute JNDs at different baselines, C reverses the meaning of a larger fraction, and D misstates Weber's law (constant ratio, not constant difference).
Question 5
A stroke destroys the primary auditory cortex in the right temporal lobe only. Audiometry is near normal in both ears, but she has difficulty locating sounds on her left side. Which explanation is correct?
- A.
  Above the brainstem each ear reaches both hemispheres, so one cortex still hears both ears, but the right cortex favours the left side of space.
- B.
  Auditory signals bypass the thalamus and reach both cortices directly, so cortical damage should not affect localisation or hearing.
- C.
  The left cochlea sends fibres only to the right cortex, so the left ear should be deaf after such a stroke, which the audiometry contradicts.
- D.
  The right medial geniculate nucleus takes over localisation after cortical damage, so no deficit should be present.
Answer: A. Above the brainstem each ear reaches both hemispheres, so one cortex still hears both ears, but the right cortex favours the left side of space.
A fits: bilateral projection preserves hearing, while a contralateral bias explains the left-sided localisation difficulty. B is wrong because auditory input relays through the thalamus. C contradicts normal audiometry in both ears. D predicts no deficit, but she has one.

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