Sensation and Perception Flashcards
Synesthesia
Two or more senses linked
Sensation
Detecting external events by sense organs and turning those into neural signals (sourness, loudness)
Perception
The more complex organizing of sensory info within the brain and the meaningful interpretations from it
What do sensory psychologists study?
Relationship between physical stimulus, psychological response, and sensory experience
Physical stimulus
Matter or energy in the world
Psychological response
Pattern of chemical and electrical activity in sense organs and CNS
Sensory experience
The subjective psychological sensation (perception)
5 major senses
Aristotle: Smell, taste, touch/pain, hearing, vision
More senses?
balance, limb position, movement
Step 1: reception
stimulation of receptors, specialized structures respond to physical stimuli and initiate neural impulses to sensory neurons
Step 2: transduction
Physical or chemical stimulation –> nerve impulses
Step 3: messages arriving in brain
Sent to many parts of brain, including specific sensory areas of cortex
Qualitative variation
Type of energy (eg. different wavelengths), activates different sets of neurons
Quantitative variation
Intensity. More/ faster action potentials
Sensory adaptation
reduction of activity in sensory receptors with repeated stimulus exposure
Gustav Fechner and William James
Psychophysics: How physical energy relates to psychological experience
Absolute threshold
Measures sensitivity, faintest detectable stimulus. Weakest amount detectable 50% of the time
Difference threshold
Depends on magnitude of original stimulus, minimal difference in magnitude between two stimuli to detect
Weber’s law
proportional difference for difference threshold
Signal detection theory
Hit, miss, false alarm, correct rejection
Purpose of perception
Identify meaningful objects as integrated wholes
How does the brain detect and integrate features?
- Feature detectors are specialized neurons to detect different individual features
- Integrate the features
Gestalt psychology
we automatically perceive whole, organized patterns, rather than parts
How do we divide a visual scene?
Figure (objects) and ground (background)
Circumscription
we detect the form surrounding the other form as the ground
Gestalt principles of grouping
tendency to organize stimuli into coherent groups (Proximity, similarity, continuity, connectedness, closure, illusory contours)
Lower threshold
Higher sensitivity
Conservative response bias vs liberal response bias
- must be sure
- more likely to say they hear it
Plasticity of perceptual systems
neurons change sensitivity/ selectivity with experience
What is the visible spectrum
electromagnetic energy that humans can detect (750 - 390 nm) –> property of sensory receptors
Wavelength
percieved as hue (colour), related to frequency (cycles/ second). QUALITY
Amplitude
max height, perception of intensity/ brightness. QUANTITY
colour purity
how many wavelengths make up the light (saturation). Spectral colours have smallest number
cornea
the transparent covering of the eye, gives the eye colour
Pupil
where light passes after cornea, hole in iris muscle
Iris
Muscle that can increase or decrease pupil size to adjust light entering
Lens
Bends the light and uses accommodation: lens thickness is adjusted by specialized muscles to change degree of light bending
Fovea
where light is focused, in retina
Retina
back of the eye, contains rods and cones. converts light energy to electrical energy
Nearsightedness
Myopia. Where faraway objects project too far in front
Farsightedness
Hyperopia. Where near object overshoots
Presbyopia
Lens gets less elastic with age
What happens when light hits photoreceptors? (Cells?)
Causes chemical changes which causes shape changes and alters ion flow in/out. Generated electricity passes to bipolar and ganglion cells which triggers action potentials
Optic nerve
Where action potentials converge, connects at the back of the retina and creates a blind spot that brain fills with info from surroundings
How is what the retina perceives different than the brain’s perceptions?
Retina senses images as upside down, flipped horizontally, and 2D, brain flips it back
Rods
-All have same photopigment type
-120 million rod cells, more in periphery
-sensitivity (ability to detect). Night vision
Cones
-3 possible pigment types (colour)
-5 million cones cells, densely clustered in fovea
-acuity (sharpness)
-more one-to-one connections
Foveation
constant eye movement to focus stimuli directly on fovea
What happens when the info from the cones gets to the brain?
Processed by visual cortex
Cortical magnification factor
fovea receive more cortical representation
hierarchical analysis
higher and higher levels create more complete representations
anatomical organization (vision)
eyes -> optic nerves -> brain -> optic chiasm
After optic chiasm
Info diverges. Axons from left of each retina go to the left hemisphere and vice versa. Axons arrive in specialized visual nucleus of thalamus then to primary visual cortex
Retinotopical organization
adjacent portions of retina go with adjacent areas of the cortex
single-cell recording
measures action potentials, determines feature detectors
After feature detectors? (Where?)
Info passed to secondary visual cortices (association) and organized into shapes. At the border of occipital and temporal lobes
Adjacent temporal (highest level)
combines basic info with more complex
Visual agnosia
vision without knowing
Ventral visual pathway
Along temporal, the “what”
Dorsal visual pathway
joins parietal, the “where” and “how”. Perception of movement processed in middle temporal cortex
Categories of movement in dorsal visual pathway
Left/right, up/down, radial
Akinetopsia
Can’t perceive motion
Sound general pathway
Vibrations -> waves -> pressure -> interpreted as sound
Human range of sound
20-20 000 HZ
Higher frequency (for sound)
Perceived higher pitch (quality)
Higher amplitude (for sound)
higher intensity/ loudness (quantity
How is a change of 10 dB perceived?
Loudness doubles
Complexity of sound
determines timbre/quality
Human voice range (Hz)
60-7000
Pinna
Outer ear, sound funnel evolved to capture sound waves. No movement so relies on structure
Canal
Enhances certain frequencies and protects tympanic membrane
Tympanic membrane
boundary between outer and middle ear, tight membrane that moves in/out with pressure changes
Ossicles
Hammer, anvil, stirrup: amplifies sound. Then oval window
Fluid in inner ear
Requires energy to move, protects inner ear by dampening vibrations
Cochlea
turns fluid vibrations to neural energy. Fluid movement causes basilar membrane to vibrate, causing cilia to bend
Cilia
triggers neural impulses. Pushing and pulling leads to action potential bursts
Pathway after cilia
Auditory nerve -> brainstem -> auditory nucleus of thalamus ->primary auditory cortex
Frequency theory
brain uses frequency of hair cell firing to indicate pitch. Does not explain how we distinguish pitch and loudness
Cilia firing
1000 times per second, alternate firing rate to achieve faster combined frequencies
Place theory
Helmholtz. Different pitches from different places along basilar membrane. High Hz beginning narrow stiff hairs, low Hz to tip (wider/ floppier). Pitch depends on where, loudness depends on how much
Frequency vs place theory
-low
-high
Tonotopic organization
maps in primary auditory cortex, high. processed near back and low near front
How does the brain use the contrast between ears
Timing and intensity to locate a sound, can detect 0.000027 second difference between ears. Better when we can see the objects
Priming
Exposure to one stimulus or multiple stimuli influences response to another stimulus (e.g. ambiguous figures)
Top-down processing
Sensory info plus other info from previous experience or larger context
Multi sensory perception
Integration of info from different senses by the nervous system
Visual dominance effect
When we get conflicting information from two senses, vision wins
Speech perception
Need both auditory and visual modalities
McGurk effect
Perceptual phenomenon that demonstrates the interaction between hearing and vision in speech perception (two pieces together make third perception)
Bottom-up processing
What we perceive based on sensory inputs (perception without additional meaning)
