The Weber-Fechner Law posits that the change in weight placed into a patient’s hand to provide a just-noticeable difference will be:
a constant ratio of the original stimulus.
For example, if the patient only notices a difference when 500 g is changed to 1000 g, then he or she will next notice a difference at 2000 g.
True or false:
Weber’s law posits that, if the smallest difference in sound noticed by a person at a given level is 2 dB, that just-noticeable difference of 2 dB will remain constant across all intensity levels.
False
Weber’s law posits that the just-noticeable difference is a constant ratio, not a constant value. Therefore, the just-noticeable difference will not be 2 dB across the board, but rather will depend on the decibel level of the original sound.
A person is carrying a 6-kg grocery bag, to which her friend is gradually adding more items. The person notices the added weight once 0.6 kg has been added. If that person were instead to hold an 8-kg bag, what would be the just-noticeable difference?
0.8 kg
The original just-noticeable difference was (0.6 kg) / (6 kg) = 0.1 = 10%. A 10% increase from 8 kg is 0.8 kg. This is a very typical Weber’s law question.
Which senses are subject to Weber’s law?
All senses (vision, hearing, taste, smell, and touch) are subject to Weber’s law.
Technically, Weber’s law doesn’t hold perfectly true at very small or very large intensity levels, but at moderate intensities, it can apply to essentially anything.
The _________ threshold is the lowest level of stimulus intensity which the body can detect.
The absolute threshold is the lowest level of stimulus intensity which the body can detect.
The _________ threshold is the amount that stimulus intensity must be changed in order for a difference to be noticeable by the person.
The difference threshold is the amount that stimulus intensity must be changed in order for a difference to be noticeable by the person.
A resident leaving a shift is walking to her car through a dark garage at night. Fearful of the desolate setting, she notices faint sounds she had not heard when she arrived in the morning. This example best illustrates:
signal detection theory.
Signal detection theory posits that our ability to detect stimuli is impacted by the intensity of the stimulus and the physical/psychological state of the individual.
In the context of signal detection, when a subject correctly identifies that a signal is present, this is termed a:
hit.
A hit occurs when a signal (such as a flash of light in an experiment) is present and the subject accurately identifies it as such.
In the context of signal detection, if a subject identifies a signal as present, but no signal had been presented at all, this is termed a:
false alarm.
A false alarm occurs when a signal is absent (for example, no light is flashed in an experiment), but the subject falsely identifies the signal as being present.
In the context of signal detection, if no signal is presented and the subject says “I didn’t see anything,” this is termed a:
correct rejection.
A correct rejection occurs when a signal is absent (for example, no light is flashed in an experiment), and the subject correctly identifies the signal as being absent.
In the context of signal detection, if a signal is presented and the subject says “I didn’t see anything,” this is termed a:
miss.
A miss occurs when a signal (such as a flash of light in an experiment) is present, but the subject mistakenly identifies it as absent.
In the 1980’s, religious fundamentalists in America protested bands like Led Zeppelin and Judas Priest, charging the bands with hiding Satanic messaging in their music that could not be consciously perceived by listeners. This exemplifies what concept?
Subliminal stimulation
Subliminal stimulation is sensory stimulation that is below the threshold for conscious perception. (Obviously, these bands were not actually hiding Satanic messaging in their lyrics, but the concept that was being complained about was subliminal stimulation.)
Define:
sensation
Sensation is the process by which human sensory receptors and the nervous system receive and represent stimuli from the environment.
Define:
perception
Perception is the process by which the body organizes and interprets sensory information, allowing recognition of meaningful stimuli.
For the MCAT, remember that sensation and perception are different concepts!
A subject sees this image and thinks, “okay, I see ears, I see two circular eyes, I see stripes…oh, this must be a tiger.” This exemplifies what form of processing?
Bottom-up processing
This process begins with sensory receptors and works up to the CNS, integrating the sensory input. Bottom-up processing usually involves detecting individual features first and later piecing them together into a coherent whole.
A motorist is driving down the highway, looking for a place to stop for the night. He sees the sign below and pulls into the parking lot. He was able to recognize his destination as a motel due to what form of processing?
Top-down processing
Top-down processing is data processing that is guided by high-level mental processes, such as when an individual draws on experience and expectations in order to form an overall perception. It is often exemplified by situations in which a person quickly recognizes an object without being able to discern all of its parts.
A medical student enters a patient’s room and recoils from the smell of feces. The attending physician, already in the room for 30 minutes, asks the medical student what is wrong, as she does not notice the smell. What adjustment has the olfactory system of the attending undergone?
Sensory adaptation
Sensory adaptation is a change over time in the responsiveness of the sensory system to a constant stimulus, in this case diminished sensitivity to olfactory stimuli as a consequence of constant stimulation.
Which type of receptor would be used to notice a flashlight at night?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Photoreceptors
Photoreceptors are used in vision to detect light.
Which type of receptor would be used to sense the smell of baby powder?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Odorant receptors
Odorant receptors detect smell.
Which type of receptor would be used to sense the presence of someone’s hand on your shoulder?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Mechanoreceptors
Mechanoreceptors detect mechanical forces, including pressure on one’s shoulder.
Which type of receptor would be used by a hand to sense an adjacent cold surface?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Thermoreceptors
Thermoreceptors detect changes in temperature.
Which type of receptor would be used when touching one’s finger to one’s nose with closed eyes?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Proprioceptors
Proprioceptors are used to detect the position of one’s own body parts in space.
Which type of receptor would be used to detect a painful needle prick?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Nociceptors
Nociceptors are used to detect painful stimuli.
Which type of receptor would be used to detect elevated systolic blood pressure?
Choose from gustatory receptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors, baroreceptors, proprioceptors, and odorant receptors.
Baroreceptors
Baroreceptors detect changes in pressure.
Which lobe of the brain is most closely associated with vision?
The occipital lobe
The occipital lobe, located at the back of the brain above the cerebellum, is most closely associated with vision. The visual cortex is found in this lobe.
Identify ocular structure A in this image.
The structure labeled A is the cornea.
See the diagram above for the identities of all labeled structures.
Identify ocular structure B in this image.
The structure labeled B is the pupil.
See the diagram above for the identities of all labeled structures.
Identify ocular structure C in this image.
The structure labeled C is the lens.
See the diagram above for the identities of all labeled structures.
Identify ocular structure D in this image.
The structure labeled D is the iris.
See the diagram above for the identities of all labeled structures.
Identify ocular structure E in this image.
The structure labeled E is the retina.
See the diagram above for the identities of all labeled structures.
Identify ocular structure F in this image.
The structure labeled F is the fovea.
See the diagram above for the identities of all labeled structures.
Identify ocular structure G in this image.
The structure labeled G is the macula.
See the diagram above for the identities of all labeled structures.
Identify ocular structure H in this image.
The structure labeled H is the optic nerve.
See the diagram above for the identities of all labeled structures.
Identify ocular structure I in this image.
The structure labeled I is the vitreous humor or vitreous gel.
See the diagram above for the identities of all labeled structures.
The variable-sized opening of the eye into which light enters is the:
pupil.
The pupil can be identified as the black region in the center of the iris, or colored portion of the eye.
The activation of the sympathetic nervous system causes the pupil of the eye to:
dilate.
To remember this, recall that the sympathetic nervous system is the “fight-or-flight” system. When under extreme stress (for instance, when one is running away from a bear), a person needs dilated pupils to let in as much light as possible to facilitate vision.
Constriction, or narrowing, of the pupils is associated with the activation of the ________ nervous system.
parasympathetic
Just as sympathetic activation causes pupil dilation, parasympathetic (“rest and digest”) activation causes pupil constriction.
What term refers to the ring of muscle that forms the colored portion of the eye and regulates pupil size?
The iris
What term refers to the biconvex structure behind the pupil that changes shape to help focus light on the retina?
The lens
In MCAT physics, you will see the lens of the eye mentioned frequently as an example of a convex lens.
What is the name of the decussating (crossed) structure which serves as the neural pathway for visual information from the environment to the primary visual cortex in the occipital lobe?
The optic chiasm
What term refers to the aspect of perceived color that is determined by the wavelength of light that hits the eye?
Hue
What term refers to the amount of energy in a light or sound stimulus, which our senses perceive as brightness or loudness?
Intensity
Which term describes the adjustment of the shape of the lens to allow the eye to focus on close or distant objects?
Accommodation
Name the two structures of the eye that are most closely involved in accommodation.
The ciliary muscle and the suspensory ligaments
In accommodation, the ciliary muscle contracts, pulling the suspensory ligaments and thereby adjusting the shape of the lens of the eye.
The difference in perception of the two images below is one of:
acuity.
Acuity is the sharpness, or clarity, of the images the eye perceives.
Define:
hyperopia
Hyperopia is an eye condition in which light is focused behind, instead of on, the retina, causing near objects to appear blurry and distant objects to appear normal.
Hyperopia is also known as farsightedness.
Identify the vision problem shown in the eye below.
The problem shown is nearsightedness (myopia).
Nearsightedness is an eye condition in which light focuses in front of, instead of on, the retina, causing distant objects to be blurry while closer objects appear normal.
What type of lens would be used to correct the visual problem shown below?
This problem, nearsightedness (myopia), would be corrected by a diverging lens.
In myopia, light converges before the retina; essentially, the lens of the eye is too strong. Utilizing a diverging lens would “cancel out” this excess convergence and correct the problem.
While this may seem like a physics question, myopia could be asked about in the context of physics or psychology. It is important that you understand topics like this one in both contexts for MCAT success.
Name the primary retinal receptors used to view an object at twilight, when ambient light is low.
Rods
Rods are retinal receptors that detect black vs. white and are necessary for peripheral and low-light vision.
Name the pigment in rods that allows for the sensation of light and dark.
Rhodopsin
Name the only photoreceptor type found at the fovea, which is responsible for color detection by the eye.
Cones
Cones are active at high light levels (photopic vision). These receptors are capable of color vision and are responsible for high spatial acuity.
What term describes the light levels at which both rods and cones are operational?
The light level where both photoreceptor types are operational is called mesopic lighting.
Most nighttime outdoor and traffic lighting scenarios are in the mesopic range.
At which point does the optic nerve exit the eye, making visual perception at that point impossible?
The blind spot
Name the specialized nerve cells in the brain which allow one to detect the shape differences between the objects below.
Feature detectors
Feature detectors are nerve cells in the brain that respond to the specific features of a stimulus, such as angle, shape, or movement.
Which type of sensory processing allows an individual to watch a video of a car and identify the shape of the car, perceive the car’s movement, and deduce the fact that the car is getting closer to the camera, all at the same time?
Parallel processing
Parallel processing is the processing of multiple stimuli or the addressing of multiple aspects of a problem simultaneously. This is important in vision, where the brain divides what it sees into color, depth, motion, and shape.
Arrange the following components of the auditory pathway into their correct sequence from the cochlea to the brain.
- Auditory cortex
- Auditory nerve
- Cochlear nuclei
- Inferior colliculus
- Superior olivary complex
- Medial geniculate nucleus
The correct pathway is:
2 (auditory nerve) → 3 (cochlear nuclei) → 5 (superior olivary complex) → 4 (inferior colliculus) → 6 (medial geniculate nucleus) → 1 (auditory cortex)
What are the three main parts of the ear?
The three main parts of the ear are the external ear, the middle ear, and the inner ear.
The ______ ear collects sound waves and funnels them down the ear canal, where they vibrate the tympanic membrane.
The external ear collects sound waves and funnels them down the ear canal, where they vibrate the tympanic membrane.
Within the ____ ear, the eardrum is connected to the ____. These are the smallest bones in the body, which mechanically carry sound waves to the ____ ear.
middle, ossicles, inner
Within the middle ear, the eardrum is connected to the ossicles. These are the smallest bones in the body, which mechanically carry sound waves to the inner ear.
The _____ connects the middle ear to the nasopharynx, equalizing the air pressure within to that of the surrounding environment.
The Eustachian tube connects the middle ear to the nasopharynx, equalizing the air pressure within to that of the surrounding environment.
The _____ ear contains the _____, the specialized organ that converts sound waves into nerve impulses that are carried to the brain via the _____ nerve.
inner, cochlea, auditory
The inner ear contains the cochlea, the specialized organ that converts sound waves into nerve impulses that are carried to the brain via the auditory nerve.
Coiling around the inside of the cochlea, the _____ contains the cells responsible for hearing. There are two types of these hair cells: _____ cells and _____ cells.
organ of Corti, inner, outer
The organ of Corti contains both inner and outer hair cells.
These specialized auditory cells are cylindrical and have stereocilia at the top of the cell and a nucleus at the bottom.
Outer hair cells
When the stereocilia (hairs) are bent in response to a sound wave, an electromotile response occurs.
Sensory information arises from the entire body. What term refers to sensation other than that associated with the five specialized senses?
Somatosensation
Somatosensation is the process that conveys information regarding the body surface and its interaction with the environment. Somatosensation is separate from the five specialized senses (vision, etc.).
Name three specialized types of somatosensation.
Somatosensation can be subdivided into:
- Mechanoreception - also called discriminative touch
- Thermoreception - temperature perception
- Nociception - pain perception, which is primarily chemical, but can also be mechanical and/or thermal
Taste can be detected via specialized sensory receptors called taste buds, which are primarily _____receptors.
chemoreceptors
Chemoreceptors detect changes in the concentrations of certain chemicals.
Scientists looking to study the effects of chemical substances produced and released into the environment by males on female behavior in social settings are most likely to measure which type of compound?
Pheromones
A pheromone is any chemical substance produced and released into the environment by an animal that affects the behavior or physiology of other members of its species. This is most commonly observed in mating.
When drinking water with a high sulfur content, people are told to hold their nose in order to reduce the bad taste of the water. This is an example of:
sensory interaction.
Sensory interaction is the idea that one sense may influence another, as when the smell or color of food influences its taste.
Name the five taste sensations detectable across the tongue.
Bitter, sour, salty, sweet, and umami
Elite athletes can often perform required movements at their peak levels, even years after retiring from their sport. This is most likely explained by the strength and duration of which sense?
The kinesthetic sense
This sense, sometimes called muscle memory, is the system for sensing the movement of individual body parts.
While considered by some sources to be essentially interchangeable with the kinesthetic sense, this term is typically used to refer to awareness of one’s body’s position in space, rather than to awareness of movement.
Proprioception
For the MCAT, you should think of proprioception as the awareness of where one’s body parts are in space (even if stationary), while the kinesthetic sense refers more to the awareness of one’s movements.
Professional bull riders have an incredibly stable sense of balance, exhibiting precise control over their position while riding the animal. This indicates they have a highly developed:
vestibular sense.
The vestibular sense is the awareness of body balance and movement. The sensations of body rotation and of gravitation and movement arise from hair cells in the inner ear.
In many animals (including humans), deprivation of light stimuli while the animal is very young can permanently stunt the development of eyesight, even if access to light is restored later. This illustrates the concept of a:
critical period.
Put simply, a critical period is a period of time during development where a given sense or skill (such as vision or language) must develop; otherwise, it will never develop properly or fully.
Which type of perceptual organization allows the brain to determine the outline of the vehicle below, even in low light?
Form perception
Form perception is the ability to recognize an object’s shape or outline.
The ability to recognize that the vehicle in the image is moving close to the camera but is not actually changing size is due to which two perceptual approaches?
Motion and constancy
Motion perception is the ability to recognize that an object is moving, while constancy is what allows the brain to understand that attributes of objects, such as color, size, and shape, are constant, even though the sensory information associated with some of these traits may change. For example, as the car approaches, it increases in size, yet we understand the car is not actually growing.
Which form of perception allows one to determine how far away an object is?
Depth perception
Depth perception is the way in which we perceive how far away objects are. Essentially, depth perception allows us to view the world three-dimensionally.
Pieces of visual information that come from both eyes working together are termed:
binocular cues.
Here, “bi-“ means “two,” while “ocular” refers to the eyes. Binocular cues include concepts such as the convergence of the two eyes on a given point in the field of vision. Such cues are required for proper depth perception.
If you close one eye, you can still gather some information about the distance of an object from you by assessing its movement relative to that of other objects in the field of view. Such pieces of information that can be gathered with one eye are:
monocular cues.
Here, “mono-“ means “one,” while “ocular” refers to the eyes. The specific monocular cue described on this card is motion parallax.
The set of principles of human perception that help us interpret and group objects are termed:
Gestalt principles.
Examples of these principles include the law of similarlity, the law of closure, and many more.
Gestalt principles in psychology are oriented around the principle of:
Prägnanz.
This principle states that, when presented with a set of elements that could be interpreted in multiple ways, people tend to perceive the simplest possible interpretation.
Which Gestalt principle is illustrated by the image below?
The principle of proximity
This Gestalt principle states that objects or shapes close to one another appear to form groups. This occurs even when the shapes, sizes, and objects are radically different, so long as they are close to each other.
Which Gestalt principle is illustrated by the image below?
The principle of similarity
This Gestalt principle states that, all else being equal, we perceive stimuli that physically resemble each other as part of the same object and stimuli that are different as part of different objects.
Which Gestalt principle is illustrated by the image below?
The principle of closure
This Gestalt principle is the tendency to see complete figures or forms even if the object shown is incomplete or partially obstructed by other objects, or if information needed to make it complete is missing.
Which Gestalt principle is illustrated by the image below?
The principle of continuation
This Gestalt principle states that when we view an image containing an intersection between two or more objects, we perceive each object as a single, uninterrupted object.
MCAT practice exams typically allow students to scroll down their viewing window to see more of the passage or question. Synchrony between the movement of the scroll bar and the passage text illustrates which Gestalt principle?
The principle of common fate
This principle states that when visual elements are seen moving in the same direction at the same rate, perception associates the movement as part of the same stimulus. The principle of common fate is used extensively in computer user-interface design.
