CH5: Sensation and Perception

Question 1

Sensation and Perception

Answer 1

Animals evolved to make use of movement to approach fitness opportunities avoid threats. The body tranforms energy from the world into information to guide us in movements. Sensation is the detection of evironmental stimuli. Perception is the recognition and identification of a sensory stimulus.

Question 2

Types of Sensation and Stimuli

Answer 2

Sensory System:
Olfactory (smell)
Somatosensory (touch)
Gustatory (taste)
Auditory (sound)
Visual (sight)

Physical Stimuli:
Odorants (airborne chemicals)
Pressure or damage to the skin
Chemicals (typically in food)
Sound waves
Light (photons)

Question 3

Thresholds are Limits of the Senses

Answer 3

Sensation relies on receptor cells being able to transduce energies from the world into electrochemical nerve signals. Signal detection theory forms the basis for analysing stimulus detection. Absolute Threshold is the least amount of energy that we can detect for a specific sense. Just Noticable Difference describes the amount of energy change required to be detected.

Question 4

Weber-Fechner’s Law

Answer 4

In the 1800’s, psychophysicists established that the relationship between stimulus magnitude and perception is not linear. Fechner’s Law describes our experienced sensations as proportional to the logarithm of the stimulus magnitude.

Question 5

Steven’s Power Law

Answer 5

Many decades later in 1957, Stanley Stevens systematically tested this relationship with many types of stimuli. This lead to the creation of the more general form called Steven’s Power Law.

Question 6

Processing Sensory Information

Answer 6

Information flows through networks in our nervous system. There are two general directions: Bottom-up and Top-down. Bottom-up processes information from the senses to “higher” regions of the brain. Tom-down processes information from higher regions of the brain to lower regions. Much of our conscious experience is a combination of sensory information with our expectations and what “should” be sensed based on prior learned experiences.

Question 7

The Chemical Senses: Smell

Answer 7

The chemical senses are the most evolutionarily ancient of all of the senses. Receptors in single cells can detect molecules in the environment for chemoattraction and chemorepulsion. Odorants in the air trigger responses in the olfactory receptor neurons. The receptor neurons send action potential signals to the olfactory bulb, which relays them to the brain. Humans have relatively weak sense of smell, but we can still detect a drop of perfume diffused in a lecture hall.

Question 8

The Chemical Senses: Taste

Answer 8

Taste works somewhat like smell. Tastants are molecules that trigger responses in taste receptor cells that make up taste buds in the tongue. Taste buds with specific compositions are found on the papillae. There are 5 types of taste receptor cells: Sweet, salt, umami, sour, and bitter. Axons that make up the gustatory nerves send taste information to the brain.

Question 9

The Tactile Senses: Somatosensation

Answer 9

Touch is a mechanical and thermal sense that results from many receptor cells in the skin, specifcally pain and temperature, and fine touch and pressure. For pain and temperature, they are the free nerve endings. For fine touch and pressure, there is the Meissner’s corpusle (touch), Merkel’s disc (fine touch), Ruffini’s ending (joint movement), Pacinian corpuscle (vibration), and Hair receptors (flutter, steady touch). Touch and pain senses are detected by receptor cells in the skin and sent to the dorsal spinal cord. From there, they ascend to the brainstem and then to the thalamus. The thalamus intergrates signals with other senses and passed somatosensory signals to the postcentral gyrus (parietal lobe).

Question 10

The Auditory Sense: Hearing

Answer 10

Hearing is a type of mechanical sense that transduces pressure changes in a medium: compression and expansion of molecules. Sound waves vary in terms of: Frequency, measured in Hz, which is percieved as pitch changes.
Amplitude, measured in pascals, percieved as loudness changes.
Phase, measured in radians, which requires two ears for sounds localization.
The wavelength of a sound is the length of one cycle of a pressure wave.
Sound first enters the outer ear, then vibrates the tympanic membrane (eardrum) and ossicles of the middle ear. The oval window vibrates, causing fluid pressure changes in the basilar membrane of the cochlea. Receptor hair cells (stereocilia) in the basilar membrane turn that pressure into action potentials. Signals are then sent into the brainstem -> thalamus -> primary auditory cortex in the temporal lobe.

Question 11

The Vestibular Sense: Balance

Answer 11

Our sense of balance (mainly head position) is inferred from the detection of fluid changes by cilia within semicircular canals found adjacent to the cochlea. Information is sent to the brainstem, thalamus, parietal cortex. There are 3 axes for directionality: Pitch, yaw, and roll. One semicircular canal for each direction in the 3D space.

Question 12

Vision: The Eye

Answer 12

Eyes have evoled in many times in animals, with most vertebrates having a common structure. A pupil that varies in size depending on lighting conditions, a flexible lens that focuses light from different distal focal points, and a retina containing photoreceptor cells that transduce light: rods and cones.

Question 13

Vision: The Retina

Answer 13

Rods are primarily used in dark light conditions and are more concentrated in the retinal periphery. Cones are primarily used in bright light conditions and are concentrated in hte retinal fovea, also used for colour vision. The fovea is the centre of our visual field and generates the highest image resolution. Photoreceptor send converging signals to bipolar cells, which send converging sinals to ganglion cells. Ganglion cell axons form the optic nerve, creating a blind spot.

Question 14

Vision: Seeing Colour

Answer 14

Colour processing is understood with complementary theories:
Trichromatic theory:
There are usually 3 distinct types of cones with peak sensitivity for different wavelengths of light. Colour results from combining them.
Opponent process theory:
Ganglion cells combine colour information from many cones and display spectral opponency (antagonistic colour-pairings) such as red-green, yellow-blue, black-white.

Question 15

The Visual Pathway

Answer 15

Visual information is sent from either:
The retina to the midbrain superior colliculus (~20%) which is used to guide eye movements.
The retina to the thalamic lateral geniculate nucleus (~80%).
Or from the LGN the primary visual cartex in the occupital lobe.
Information from each visual hemifield (left vs. right of the centre) is processed in the opposite cerebral hemisphere.

Question 16

Visual Processing “Above” V1

Answer 16

More complex aspects of vision are processed in “higher” regions of cortex along two streams:
The dorsal “where” stream is where information about object location and motion are processed along pathways toward the parietal lobe.
The ventral “what” stream is where information about object identity and category are processed along pathways toward the temporeal lobe.
Both streams are in constant communication to update each other about “where” and “what” information.

Question 17

Top-Down: Gestalt

Answer 17

Visual scenes are constructed through a combination of visual input from the retina (bottom-up) and expectations from “higher” regions of the visual cortex (top-down). Gestalt principles involve top-down expectations about what a scene or object “should” look like based on familiar or limited features.

Question 18

Depth Perception

Answer 18

Our ability to percieve depth in a scene is a result of combination of monocular and binocular cues. Monocular cues are visual clues about depth and distance that can be percieved with one eye, like light and shadow, clarity, familiar size, etc. Binocular cue rely onretinal disaprity, which is the slight difference in image on each eye.