Perception 2 Flashcards
Sensory adaptation
A decrease in sensory receptor sensitivity to a constant stimulus helps us ignore unchanging information.
Sensory systems respond less to repeated stimuli.
The brain interprets the proximal stimulus based on changes, not fixed values.
Context affects perception early in the sensory process.
Visual( Ganglion cells) adaptation
adapt their firing rate to ambient light levels.
In bright light, they need stronger stimuli to respond.
They detect changes in brightness rather than absolute light levels.
Weber’s Law
The just noticeable difference (JND) is the smallest change in a stimulus that can be detected.
JND depends on the stimulus magnitude: ∆I / I = K (Weber’s Law).
K (Weber fraction) varies by sense:
Loudness: ≈ 0.05
Brightness: ≈ 0.08
Heaviness: ≈ 0.02
Auditory adaptation &
Weber’s law
Auditory Adaptation: The ear becomes less sensitive to constant or repeated sounds.
Weber’s Law: A ~5% change in sound intensity is needed to notice a difference.
Examples:
Tuning out background noise (like an air conditioner).
Noticing volume changes more in quiet settings than in noisy ones.
Somatosensory system (weight and Weber’s law
JND in Weight: ~2% of the
object’s weight
I = 𝐾 4/ 200 = 0.02 2%
- Heavier objects require greater
changes to detect differences
Somatosensory
adaptation
- SA = slow adapting
- RA = rapid adapting
A receptive field is the area of a sensory surface that a neuron responds to( Acuity)
Smaller receptive fields → Higher acuity (sharp perception).
Larger receptive fields → Lower acuity but respond to more complex stimuli.
Higher-order neurons process broader and more complex sensory information.
Visual receptive
fields( photoreceptors and Retinal ganglion cells)
Each neuron after photoreceptors processes input from multiple photoreceptors.
Retinal ganglion cells gather signals from bipolar and amacrine cells to detect patterns and contrast.
Visual receptive fields ( Ganglion cells, LGN. V1)
Ganglion cells: Detect contrast with center-surround fields
.
LGN: Keeps center-surround organization
.
V1 neurons: Respond to edges and orientation
Ganglion cell ( Action)
Action potentials of ganglion cell and At rest, ganglion cells is firing at some baseline level
ganglion cell / Light falls outside
There is no change in response when light falls outside the receptive field of a ganglion cell.
Light at center of receptive field.
= increased firing rate.
No Change when Ganglion cells
There is no change in the ganglion cell’s response when light falls outside its receptive field.
Ganglion cells/ falls on the surrounding Light
When light falls on the surrounding area that inhibits the cell, the cell’s response decreases further.
Auditory of a hair cell
Receptive field of a hair cell: frequency of sound.
Somatosensory receptive fields( mechanoreceptor, Suface, Deeper)
The receptive field of a mechanoreceptor is the area on the skin that the receptor responds to:
Surface receptors: Smaller receptive fields.
Deeper receptors: Larger receptive fields.
Somatosensory
receptive fields/ body, Back, Thigh, Foot.
Receptive field size and acuity vary across different body parts:
Back: Larger receptive fields, lower acuity.
Thigh: Moderate receptive field size and acuity.
Foot: Smaller receptive fields, higher acuity.
Somatosensory
Lateral inhibition enhances contrast by
allowing neurons to adjust their signals, making sensory information more distinct.
Topographic maps
show how sensory information is organized in the brain, with nearby sensory areas mapped to nearby brain regions.
Retinotopic map
How is visual information organized in primary visual cortex? Ret, Hierarchically, V1, LGN
Retinotopically: Neighboring areas on the retina map to neighboring areas in V1
Hierarchically: Visual info flows through V2, V3, V4, V5 (MT).
V1: Processes initial visual features.
LGN to V1: LGN sends visual info to V1 for recognition
Retinotopic Map
organizes retinal information in the brain, with Neighboring retina areas mapped to V1 areas.
Tonotopic( Auditory) Maps
A tonotopic map is a fundamental organizing principle in the auditory system. It represents the mapping of different sound frequencies to specific spatial locations.
Somatotopic maps
A somatotopic map links body parts to the somatosensory cortex. Somatotopy is this point-for-point mapping.
Somatosensory homunculus
It is a cortical homunculus, which is a map of the body’s surface on the somatosensory cortex in the brain. The somatosensory cortex is arranged such that a particular location receives information from a particular part of the body.
How flexible are cortical maps? Can
they change?
cortical maps are flexible and can change through neuroplasticity. They can reorganize based on learning, experience, injury recovery, and sensory changes.
Reorganization of
retinotopic map(A lesion in the visual field (in both eyes) causes )
reorganization in the primary visual cortex.
Tinnitus:
perception of sound in absence of auditory stimulation
Potential Damage to the Cochlea
Damage to the cochlea, auditory pathway, or brain areas can cause the brain to reorganize, leading to spontaneous neuron firing and phantom sounds like tinnitus.
Reorganization of somatotopic maps & missing limb
Reorganization of somatotopic maps occurs when brain areas adjust after limb loss, leading to changes in sensory representation. This can cause phantom limb sensations, where the brain still “feels” the missing limb due to the reorganization of the sensory cortex.
Hierarchical Organization lower-to higher- order neurons.
Sensory processing moves from lower- to higher-order neurons.
Serial: Step-by-step.
Parallel: Simultaneous.
Recurrent: Feedback loops.
Hierarchy in Visual system( SPRM)
Serial: Info flows from V1 to V2 and beyond.
Parallel: Different visual aspects (motion, color, etc.) are processed at the same time in areas like V3, V4, V5.
Recurrent: Feedback loops refine processing in areas like MST and VIP.
Modularity: Specialized areas handle different visual info before integration.
meaning of Feature detectors and tuning curves.
Feature detectors are neurons that respond to specific visual stimuli. Tuning curves characterize sensory neuron responses.
Example: Orientation feature detectors in V1.
Combine center-surround neurons to
detect specific edge orientations in V1.
Cortical column ( V1 and Blobs)
V1 (primary visual cortex) has columns that detect object orientations:
Each visual field location has columns for all angles.
Ocular dominance columns for each eye.
Orientation columns for different angles.
Blobs specialize in color processing.
Oriented lines of a specific length in V2
V2 refer to simple cells that respond to lines of particular width, orientation, angle, and position within the visual field.
how people experience a space these and
can create visual interest, balance, harmony, and convey meaning and emotion.
Visual hierarchy principles( S C P T B A R :
Size: Use larger elements to draw attention.
Color & Contrast: Highlight key elements.
Perspective: Add depth and separation.
Typefaces: Choose impactful fonts.
Balance & Symmetry: Direct focus.
Alignment & Proximity: Group related items.
Reading Patterns: Guide the viewer’s focus.
Hierarchy in auditory system ( Modularity system)( A1, A2, Parabelt, Multmodal)
Auditory system modularity:
Primary auditory cortex (A1): Processes sound.
Secondary auditory cortex (A2): Analyzes sound further.
Tertiary auditory cortex (Parabelt): Handles higher-level processing.
Multimodal cortex: Integrates sound with other senses.
Directional Tuning in the Superior Colliculus
In superior colliculus of ferret
Different neurons respond to sounds coming from different directions.
Numbered areas: Directional tuning curves for individual neurons in superiors colliculus.
Amplitude dark green to Amplitudes dark red.
Auditory directional feature detectors.( ITD)
When sound comes from a non-central source, it reaches each ear out of phase.
Interaural Time Difference (ITD): The small difference in arrival time of sound between the two ears helps determine the horizontal location of the sound source.
ITD( localize sound)( Coincidence detectors)
ITD: Locates sound horizontally.
Coincidence detectors: Fire when both ears receive sound simultaneously.
Right source: ITD > 0 (left ear later).
Center source: ITD = 0 (both ears same time).
Left source: ITD < 0 (right ear later).
Auditory directional feature ( Coincidence deterctors)
Coincidence detectors: Neurons in the superior olivary nucleus (in the pons) fire when signals from both ears arrive at the same time, helping to determine the sound’s location.
Somatosensory system modularity( Primary, secondary, Tertiary, Multimodal)
S1 (Primary Somatosensory Cortex - BA 1, 2, 3): First stage of touch and body sensation processing.
S2 (Secondary Somatosensory Cortex - PV): Further processing and integration.
Tertiary Somatosensory Cortex (BA 5, MIP, AIP): Higher-level processing and association.
Multimodal Association Cortex (VIP, etc.): Combines touch with other senses.
Somatosensory orientation feature detectors in S2 ( Touch)
- respond to touch along a specific direction in specific part of skin
Somatosensory orientation Pressure Detectors.
Combine simple touch or pressure detectors to form somatosensory orientation feature detectors, enabling complex angle detection.
Somatosensory motion detectors in S1( M O D )
Motion-sensitive: Detect any movement.
Orientation-sensitive: Detect motion along a specific axis.
Direction-sensitive: Detect motion in one direction.
what pathway( ventral stream) and where pathway( dorsal stream)
The ventral stream (“what” pathway) is responsible for identifying and recognizing objects, leading to the temporal lobe.
The dorsal stream (“where” pathway) determines the positional location of objects and guides actions related to them.
Face sensitive and Damage
Face-sensitive cells in the FFA of the IT cortex.
Damage to FFA= Prosopagnosia( inability to perceive faces)
Visual Streams( A, M, L, V, and DAMAGE)
Intraparietal sulcus (IP):
Anterior (AIP): Hand movement space.
Medial (MIP): Arm movement space.
Lateral (LIP): Eye movement space.
Ventral (VIP): Facial movement space.
Damage: Spatial attention deficits, neglect.
V5 (MT): Motion detection.
Damage: Akinetopsia (motion blindness).
Somatosensory what( Ventral)Bottom-up:
& where streams( Dorsal)Top-down:
The visual hierarchy splits into ventral (“what”) and dorsal (“where”) streams:
Bottom-up: Input flows retina → LGN → V1 → higher areas.
Top-down: Higher areas shape perception via knowledge, attention, and expectations.
Bottom-up and Top-down Feedforward connections
Stimulus-driven (Bottom-up):
Feedforward connections process raw sensory input based on the stimulus and genetic wiring.
Top-down:
Feedback connections shape perception based on goals, expectations, and past experiences.
Bottom- up processing( example)
For example, if you see a white and brown house, bottom-up processing would focus on the brown color first, building the perception from the basic visual elements.
Top Down processing drawing of the man
A drawing of a man involves processing the black areas in the image.
Top-down processing Drawing of the man
Now you are seeing the more defined drawing really seeing the man
Likelihood or most likey principle:
We perceive the world in a way that is “most likely” based on our past experiences
Interactive
activation model.
The model assumes that the processing of information during reading consists of series of levels corresponding to visual features, letters and words.
Interactive Activation
Theory: McClelland
and Rumelhart.
Model of letters and word perception
Integrates bottom-up and top-down processes.
Bottom-up processing and Excite letters
Excite letters: A non-standard handwriting pattern formed from the bottom up, avoiding downstrokes.
Bottom-up processing: Perception built entirely from sensory input, without prior knowledge or expectations.
processes are necessary to explain perception.
Both bottom-up and top-down processes are necessary to explain perception.
