Week 4 Flashcards
Sensation & transduction
Sensation: Stim of sense organ
Transduction: receptors convert physical from environment to signals for brain to interpret
Perception
Interpretation of a sensation –> mental representation
Sensory adaptation
Sensitivity to prolonged stim tends to decline over time as one adapts to current conditions
Psychophysics
Study of how physical stim affect the senses
Absolute threshold
Minimal intensity needed to barely detect a stim 50% of the time
Sensitivity
How responsive one is to faint stim
Acuity
Differentiating btw two stim (e.g. two similar tones)
Just noticeable difference (JND)
Minimal change in a stim that can barely be detected
Weber’s law
Amount of change needed for change to be noticed is constant ratio of the original stim
Signal detection theory
Response to a stim depends on person’s sensitivity to stim and a person’s decision critereon
How is light interpreted in the eye?
(keywords: cornea, pupil, iris, lens, accommodation, retina, photoreceptor cells, optic nerve)
1) Light passes through CORNEA (clear protective layer around eye)
2) Light passes through PUPIL (hole in the IRIS, the colored part of the eye that controls how much light is let in)
3) Light passes through LENS, which is shaped by eye muscles so the light is focused on the RETINA in a process called ACCOMMODATION (lens flatter for objects further away, lens more curved for objects nearby)
4) Retina lined with PHOTORECEPTOR CELLS called RODS and CONES
5) Signals from rods and cones transducted to brain via the OPTIC NERVE (OPTIC DISK is the beginning of the nerve in the eye)
Myopia vs hyperopia
Myopia/nearsighted - eyeball too long –> image focused in FRONT of retina
Hyperopia - eyeball too short –> image focused BEHIND retina
Rods
- Peripheral and night vision, brightness
- More rods than cones (~120M rods)
- Distributed evenly in retina except for area in the macula called the FOVEA
- No rods in fovea –> reduced clarity in low light but increased sensitivity to light in periphery
Cones
- C words - “Clarity and Color”
- ~6M cones; concentrated in the FOVEA but sparse in macula/retina –> we see things much clearer if we look right at them
- 3 different cones for 3 different wavelengths: L-cones (long - red), M-cones (medium - green), S-cones (short - blue)
- Missing cones –> color blindness
Trichromatic color theory
We perceive color by combining RGB wavelengths
Color-opponent system
Pairs of cone types work against each other
What causes negative afterimages?
Opponent process theory: cones are together in opposing pairs: red/green, yellow/blue, black/white
- Cells stimulated by green inhibit the cells stimulated by red
- When changed, the previously inhibited red cells fire, while the green PREVIOUSLY-stimulated cells are tired and don’t fire –> we see red
Neurological pathway from photoreceptor cells to brain
rods/cones –> bipolar cells –> retinal ganglion cells –> lateral geniculate nucleus (part of thalamus) –> area v1 –> other parts of the brain
NOTE: bunded RGCs form the optic nerve
Dorsal vs ventral vision pathways + purpose
Dorsal: “where” – where an object is and its movement; upper pathway to parietal lobe
Ventral: “what”/”how” – shape and identity of an object; lower pathway to temporal lobe
Purpose: Neurons in area v1 only perceive small details like edge –> signals to regions farther from V1 respond to more complex features
Visual agnosia vs prosopagnosia
Visual agnosia: inability to recognize objects
Prosopagnosia: inability to recognize faces
Patient DF
Injured ventral stream –> couldn’t recognize objects
Bottom-up processing
Sensory receptors pick up signals and send them to the brain
Top-down processing
Perceiving things based on your prior knowledge of the world
Monocular/pictorial depth cues
- Can be seen w one eye
- Linear perspective/vanishing point, light and shadow, interposition, relative height, relative size, texture gradient
Binocular depth cues
- Both eyes
- RETINAL DISPARITY - two retinas have slightly different views of the world
- CONVERGENCE - when a person perceives an object as close, eye muscles make the eyeballs turn in more – brain perceives
Perceptual constancy
Even as aspects of sensory signals chance, our perception of it doesn’t
Conceptual knowledge
- When we perceive an object, we not only recognize what it looks like but also what it is/what it’s doing
- Ex: when we see a car coming towards us we not only recognize it as a car but also that it’s metal, it could hurt us, it’s moving fast, etc
Perceptual organization
Process of grouping or segregating features to organize objects
Perceptual grouping rules
PSSCCC
- Proximity: objects grouped together are associated w each other
- Simplicity: simplest interpretation of objects
- Similarity: similarities in texture, shape, etc
- Continuity: tend to group objects w good continuation (edges or contours w same orientation)
- Closure: fill in missing gaps of visual scene
- Common fate: elements of a visual object moving together are perceived as parts of a single moving object
Change blindness vs inattentional blindness
Change blindness: fail to notice change in visual scene
Inattentional blindness: fail to perceive objects not the focus of attention
Muller-lyer illusion
Length of a line appears to be dependent on the orientation of arrows
Carpentered world hypothesis
prev experience w corners plays role in the strength of muller-lyer illusion
Point of subjective vs objective equality
Point of subjective equality: Point at which the two lines APPEAR equal
Point of objective equality: point at which the two lines are ACTUALLY equal
How are sound waves interpreted as sound in the brain?
(keywords: pinna, auditory canal, eardrum, ossicles, cochlea, basilar membrane, inner hair cells)
1) The PINNA collects and channels sound waves into the AUDITORY CANAL, which funnels sound into the EARDRUM
2) The EARDRUM vibrates in response to the soundwaves
3) The OSSICLES (3 bones – hammer, anvil, and stirrup) amplify the vibrations to the COCHLEA
4) The COCHLEA converts the vibrations into neural impulses
- Cochlea divided by structure called BASILAR MEMBRANE – low frequency = tip moves, high frequency = base moves
- Basilar membrane moves up and down –> moves cochlear fluid –> stimulates INNER HAIR CELLS
5) INNER HAIR CELLS (specialized auditory receptor neurons located on basilar membrane) send signal to auditory nerve –> thalamus –> A1 (temporal lobe)
- Some evidence also suggests dorsal and ventral auditory streams
McGurk effect
Speaker’s lip movements influence what sound is heard
What are the physical dimensions of a soundwave
Frequency: pitch – measured in hz
Amplitude: intensity/loudness – measured in dB
Complexity: influences measure of timbre (quality that lets you differentiate btw note on piano vs guitar, etc) – mixture of soundwaves
What are the different parts of the outer ear, middle ear, and inner ear?
Outer ear: pinna, auditory canal, eardrum
Middle ear: ossicles (hammer, anvil, stirrup)
Inner ear: cochlea (contains basilar membrane + inner hair cells), auditory nerve
How is pitch signaled to the brain (2 “codes”)
Place code: brain uses relative activity of hair cells across whole membrane to determine pitch
Temporal code: brain uses timing of APs to determine pitch
How is loudness signaled to the brain
Total amount of hair cell activity
How is timbre signaled to the brain
Relative activity of hair cells
How is location signaled to the brain
Binaural cues: sound arrives at one ear sooner than the other + sound will be more intense in one ear than the other
Conductive vs sensorineural hearing loss
Conductive hearing loss: damaged eardrums or ossicles; can be corrected w surgery
Sensorineural: damage to inner ear; sensitivity and acuity decrease; hearing can help w sensitivity issues but not accuity
