- A 100 g weight just noticeably differs from a 104 g one. What is the Weber fraction?
Answer: 0.04
The Weber fraction is the just noticeable difference divided by the original stimulus. The difference is 104 minus 100, which is 4 g, and the original weight is 100 g, so 4 / 100 = 0.04. The tempting error is choosing 4.00 because that is the raw difference in grams, but you must divide by the original weight to get the fraction.
- A faint tone is detected on 3 of 6 trials. Its intensity is:
Answer: At the absolute threshold
Detecting a tone on 3 of 6 trials is 50 percent detection, which defines the absolute threshold: the intensity at which a stimulus is detected half the time. The tempting answer is subliminal tone intensity, but subliminal means below threshold and would be detected less than 50 percent, not exactly half.
- An audiologist determines that a participant's absolute threshold for a specific tone is 10 decibels. Which of the following is the most accurate interpretation of this finding?
Answer: The participant will report hearing the tone on approximately 50% of the trials when it is presented at 10 decibels.
The absolute threshold is defined statistically, not as a fixed, all-or-none point. It is the minimum stimulus intensity that an organism can detect 50% of the time. Therefore, at 10 decibels, the participant's detection of the tone is expected to be at chance level.
- A researcher is studying visual perception. Which of the following experimental changes would most likely increase a participant's sensory sensitivity (d'), rather than simply altering their response bias (beta)?
Answer: Replacing a blurry, low-contrast monitor with a sharp, high-contrast monitor.
Sensory sensitivity (d') reflects the observer's actual ability to discriminate a signal from noise. Improving the quality of the stimulus itself (e.g., by using a clearer monitor) makes the signal easier to distinguish from the background noise, thus directly increasing d'. The other options manipulate motivation, expectation, or instructions, all of which change the response bias (beta) without affecting the underlying sensory capability.
- A coffee taster is attempting to determine which of two cups of coffee has a slightly higher concentration of a certain flavor compound. The taster sips from one cup, then the other, repeating until they can reliably identify the stronger cup. This procedure is an attempt to measure a:
Answer: difference threshold.
The taster is not determining the minimum amount of flavor they can detect from nothing (absolute threshold). Instead, they are trying to find the minimum detectable difference between two already existing stimuli (the two cups of coffee). This is the definition of a difference threshold, or just noticeable difference (JND).
- During dark adaptation, the absolute threshold for light:
Answer: Decreases as sensitivity rises
Dark adaptation makes your eyes more sensitive to light, so you need less light to detect a stimulus. The absolute threshold is the minimum light needed, so as sensitivity rises, that minimum falls. A tempting error is thinking threshold and sensitivity move together, but sensitivity rising means threshold dropping, not increasing.
- Which of the following statements best articulates the fundamental role of transduction in the broader process of perception?
Answer: Transduction serves as the translation step, converting external physical energy into the internal neural language used for perception.
Perception is the brain's process of interpreting sensory information. For this to happen, the external world's physical energy (light, sound, pressure, chemicals) must first be converted into electrochemical signals that neurons can process. This conversion, or translation, is the specific and essential role of transduction.
- A food scientist determines that the Weber fraction for the taste of sugar in water is 0.10. If the just noticeable difference (JND) for a new beverage is found to be an addition of 3 grams of sugar, what was the original amount of sugar in the beverage?
Answer: 30 grams
Weber's Law is expressed as ΔI = k * I, where ΔI is the JND, k is the Weber fraction, and I is the original stimulus intensity. The problem provides ΔI = 3 grams and k = 0.10. To find the original intensity (I), the formula is rearranged to I = ΔI / k. Therefore, I = 3 grams / 0.10 = 30 grams.
- A new air traffic controller is trained to be extremely cautious, reporting any radar blip that could possibly be an unauthorized aircraft. According to signal detection theory, this cautious response strategy will most likely affect the controller's performance by increasing the number of:
Answer: hits and false alarms.
Adopting a cautious or liberal response criterion (i.e., being more willing to say 'yes, there is a signal') increases the likelihood of detecting true signals (hits). However, it also inevitably increases the likelihood of incorrectly identifying noise as a signal (false alarms). This represents a shift in response bias, not sensory sensitivity.
- A chef finds they must add 5 grams of a spice to a 100-gram dish for its flavor to be just noticeably stronger. According to Weber's Law, if the chef prepares a 400-gram version of the same dish, how much of the same spice must be added for the flavor to be just noticeably stronger?
Answer: 20 grams
Weber's Law states that the just noticeable difference (JND) is a constant proportion (k) of the original stimulus intensity (I). In this case, the proportion is k = 5g / 100g = 0.05. To find the JND for the 400-gram dish, we multiply this constant by the new intensity: JND = 0.05 * 400g = 20g.
- While sensory adaptation is a common feature of most sensory systems, it is notably reduced for stimuli indicating intense pain. From a functional, evolutionary perspective, what is the most likely reason for this exception?
Answer: The continued perception of a pain signal is often critical for avoiding further injury and promoting healing.
Sensory adaptation allows an organism to ignore constant, non-threatening stimuli and remain alert to changes. Pain signals ongoing tissue damage. If an organism were to adapt to this signal and cease to perceive it, they might engage in behaviors that worsen the injury. Therefore, the lack of adaptation for intense pain is highly adaptive for survival.
- An individual moves into an apartment next to a hospital and is initially bothered by the frequent sound of sirens. After a few weeks, they no longer have a strong emotional or attentional reaction to the sound. This change is best described as habituation. How would this differ from sensory adaptation to the sound?
Answer: Sensory adaptation would involve the hair cells in the cochlea becoming less sensitive to the specific frequency of the siren.
The key distinction is physiological versus cognitive. Sensory adaptation is a 'bottom-up' process involving a change in the responsiveness of the sensory receptors themselves. Habituation is a 'top-down' form of learning where the brain learns to ignore a repeated, unimportant stimulus. Choice A correctly identifies the physiological change at the receptor level (hair cells) that would characterize sensory adaptation.
- Which of the following pairs correctly identifies a sensory receptor cell and the primary sensory process it initiates?
Answer: Rod and cone cells; transduction
Rod and cone cells are the photoreceptors of the retina. Their fundamental function is to absorb photons of light and convert (transduce) that light energy into a change in membrane potential, which is the first step in creating a neural signal for vision. The other options mispair the cell with the process.
- A neuro-engineer is designing a prosthetic limb that can experience a sense of touch. The device has sensors that can accurately measure pressure and temperature, and it has a direct interface with the somatosensory cortex. However, clinical trials fail, with patients reporting no tactile sensations. The failure is most likely due to an omission of a component that performs which of the following processes?
Answer: Transduction
Transduction is the critical process of converting stimulus energy (like pressure or heat) into neural impulses that the brain can understand. The device can measure the physical properties but lacks the mechanism to convert that physical data into the electrochemical language of the nervous system, which is why the brain cannot perceive it.
- After wearing a new ring for several days, an individual no longer feels its presence on their finger, unless they consciously think about it. Which of the following provides the best physiological explanation for this change in sensation?
Answer: The touch receptors in the skin have reduced their firing rate in response to the continuous, unchanging pressure.
This scenario describes sensory adaptation, which is a physiological process where sensory receptors become less responsive to a constant, unchanging stimulus. The reduced firing rate of the touch receptors is the direct cause of the diminished sensation. Habituation is a cognitive process of reduced attention, not a physiological change at the receptor level.
- A researcher presents light stimuli of varying intensities to a subject and records the percentage of trials on which the subject reports seeing the light. The data show detection rates of 10% at 4 units, 30% at 6 units, 50% at 8 units, and 80% at 10 units. Based on these data, the subject's absolute threshold for this light is:
Answer: exactly 8 units.
The absolute threshold is operationally defined as the stimulus intensity that is detected 50% of the time. According to the data provided, the light with an intensity of 8 units was detected on exactly 50% of the trials, making it the absolute threshold.
- A person spends 30 minutes in a very dark room (dark adaptation). They are then moved to a dimly lit room and asked to distinguish between gray squares of slightly different shades. Compared to a person who had just come from a brightly lit office, the dark-adapted person will have:
Answer: a lower absolute threshold and a smaller difference threshold for light.
Dark adaptation increases the sensitivity of the visual system, primarily by regeneration of photopigments in the rods. This increased sensitivity means that 1) a weaker light can be detected, so the absolute threshold is lower, and 2) smaller changes in light intensity can be discriminated, so the difference threshold (JND) is smaller.
- In the human ear, the mechanical vibration of the stapes against the oval window causes fluid to move within the cochlea. This fluid movement, in turn, causes the basilar membrane to vibrate, bending hair cells. This bending of hair cells is the critical event for hearing because it is the point at which:
Answer: mechanical energy is transduced into a neural signal.
The entire sequence of events prior to the bending of hair cells involves the transmission and amplification of mechanical energy. The bending of the hair cells is the pivotal moment of transduction, where this mechanical force is converted into an electrical change in the cell's membrane potential, which initiates a neural signal.
- In a signal detection task, a participant initially demonstrates a conservative response bias, resulting in a low number of hits but also a very low number of false alarms. If the experimenter successfully modifies the participant's strategy to be more liberal, which outcome is expected?
Answer: A decrease in misses and a decrease in correct rejections.
A conservative bias means the participant is reluctant to say 'signal present', leading to few hits and few false alarms, but many misses and many correct rejections. Shifting to a liberal bias means they say 'signal present' more often. This will increase hits (reducing misses) but will also increase false alarms (reducing correct rejections).
- What is the immediate result of sensory transduction?
Answer: A graded receptor potential
Sensory transduction converts a stimulus into a local change in membrane potential, called a graded receptor potential. This happens before any action potential is triggered, since action potentials occur only if the graded potential reaches threshold. The most tempting wrong answer is an action potential in a nerve, but that is a later step, not the immediate result of transduction.
