Sensation and Perception

Question 1

Sensation and Perception

Answer 1

• Sensation: Transduction of physical, electromagnetic, auditory, and other information from internal and external environment and converting it into electrical signals in nervous system (raw unprocessed signal).
• Perception: Processing of this information within central nervous system to make sense of the information’s significance.

Question 2

Sensory Receptors

Answer 2

• Distal Stimuli: Objects producing stimuli that interact directly with sensory receptors.
• Proximal Stimuli: Sensory-stimulating byproducts of distal stimuli.
• Campfire is distal stimuli, photons and sound produced by fire are proximal stimuli.
• Photoreceptors (EM waves), mechanoreceptors (pressure/movement for hearing and acceleration), nociceptors (pain), thermoreceptors, osmoreceptors, olfactory receptors, taste receptors.

Question 3

Threshold

Answer 3

• Threshold: Minimum amount of stimulus that renders a difference in perception. Temp difference noticeable when sun sets, but subtle changes throughout day are unnoticed.
• Absolute Threshold: Minimum of stimulus energy needed to activate a sensory system (to convert stimulus into action potential).
• Threshold of Conscious Perception: Level of intensity that a stimulus must pass in order to be consciously perceived by brain. Subliminal Perception is information not perceived by brain, as stimulus intensity not high enough.
• Difference Threshold (Just-Noticeable Difference): Minimum change in magnitude of two stimuli required to perceive the difference between the two; reported as a fraction or percent, since JNDs are proportional (Weber’s Law). Discrimination testing used to determine JND.

Question 4

Signal Detection Theory

Answer 4

• Signal Detection Theory: Study of how internal (psychological) and external (environmental) factors influence threshold of sensation and perception.
• Experiments consist of noise trials (signal presented) and catch trials (signal absent) and subject asked to indicate whether signal was present or not. Outcomes include hit (correctly perceived presented signal), miss (failed to perceive presented signal), false alarm (incorrectly perceived absent signal), correct negative (correctly did not perceive absent signal).
• Adaptation: Stimuli detection changes over time. Cold water no longer cold after you get used to it, and pupils dilate in dark to adapt to light change.

Question 5

Eye

Answer 5

• Accommodation: Suspensory ligaments pull on the lens, flattening or thickening it to focus on an image as distance varies.
• Duplicity Theory of Vision: Cones permit color vision and fine detail sensing and are most effective in bright light conditions. Rods permit light-dark sensation with low resolution and are most functional in low light conditions.
• Concentration of cones increases as center of retina is approached (macula has high cone concentration, and fovea contains only cones). Concentration of rods increases as distance from fovea increases. Visual acuity best at fovea.
• Blind Spot: Region of retina devoid of photoreceptors where optic nerve leaves eye.
• Rods and cones synapse directly with bipolar cells, which synapse with ganglion cells, the axons of which form the optic nerve.
• Visual Pathways: Each eye’s left visual field projects onto right side of each eye’s retina, and vice versa. Signal travels down optic nerve until optic chiasm is reached, where nasal half of each retina cross over (temporal fibers do not cross over). Fibers from right side of retina project onto right side of brain, and vice versa. Therefore, each eye’s left visual field projects onto right side of brain. Pathways called optic tracts once they leave optic chiasm. Fibers of optic tracts go to superior colliculus of midbrain and LGN of thalamus then to visual cortex in occipital lobe.
• Parallel Processing: Brain’s ability to analyze information regarding color, form, motion, and depth simultaneously using independent pathways. Color detected by cones; Form detected by parvocellular cells (high spatial resolution for detecting fine detail, but low temporal resolution so only stationary or slow objects can be viewed in detail); Motion detected by magnocellular cells (high temporal resolution for detecting motion, but low spatial resolution so only blurry image provided for moving objects); Depth detected by binocular cells that compare discrepancies between inputs from both eyes to each hemisphere.

Question 6

Ear

Answer 6

• Pinna/auricle channels sound waves into external auditory canal to tympanic membrane (which divides outer ear from middle ear).
• Middle ear contains ossicles (malleus, incus, stapes) and Eustachian tube (connects to nasal cavity to help equalize pressure between middle ear and environment).
• Endolymph-filled membranous labyrinth is suspended within bony labyrinth by perilymph. Cochlea houses organ of Corti (hearing apparatus composed of hair cells that transduces sound waves into electrical signal to be carried by vestibulocochlear nerve); Vestibule contains balancing apparatus this is sensitive to linear acceleration and that determines 3-D orientation; Semicircular Canals contains hair cells that are sensitive to rotational acceleration.
• Auditory Pathways: Vestibulocochlear nerve travels to brainstem, where it ascends to inferior colliculus of midbrain and MGN of thalamus then to auditory cortex in temporal lobe.
• Place Theory: Theory of sound perception which states that the location of a hair cell on the basilar membrane determines the perception of pitch when that hair cell is vibrated; cochlea is tonotopically organized.

Question 7

Object Recognition

Answer 7

• Bottom-Up Processing: Object recognition by parallel processing and feature detection (individual sensory stimuli combined together to create cohesive image).
• Top-Down Processing: Object recognition driven by memories and expectations (allows quick recognition of objects without needing to analyze specific parts).
• Deja Vu occurs when recognition occurs through top-down processing seemingly without obvious reason in a situation where bottom-up processing is expected to occur.
• Gestalt Principles: Governed by Law of Pragnanz which states that perceptual organization will always be as regular, simple, and symmetric as possible; Law of Proximity (a. elements close to one another tend to be perceived as a unit); Law of Similarity (b. similar objects tend to be grouped together); Law of Good Continuation (c. elements that appear to follow in the same pathway to be group together); Subjective Contours (d. perceiving contours and shapes that are not actually present in the stimulus); Law of Closure (e. space tends to be perceived as a complete figure when enclosed by a contour).