Sensation and Perception Flashcards
Sensation definition
Process by which sensory receptors and nervous system receive and represent stimuli
Perception definition
Process of organizing and interpreting sensory information
Bottom-up processing
- Data-driven
- Begins with incoming sensory information and continues to perception
Top-down processing
- Concept-driven
- Using pre-existing interpretation to interpret incoming sensory information
Vision
Light waves absorbed by photoreceptors in retina
Two types of photoreceptors
- Cones - bright lights, visual acuity, colors
- Rods - dim lights, peripheral vision
Visual acuity
Sharpness and precise detail
Two main theories of color vision
- Trichromatic theory
- Opponent process theory
Trichromatic theory
- Retina contains red, blue, green cones
- Related to initial processing in retina
Opponent process theory
- Red/green, blue/yellow, white/black cells
- Related to processing beyond retina
- Explains afterimages, blue/yellow colorblindness
Color Blindness
- Red/green most common - usually due to genetics but can be due to disease/injury
- Blue/yellow - due to genetics
Red/green color blindness (genetic mutation)
- Recessive gene on X chromosome
- More common in males (only have one X and only need one gene) than females (have two X and need gene on both)
Blue/yellow color blindness (genetic mutation)
- Autosomal (non-sex) dominant gene
- Affects males and females equally
Depth perception
Depends on binocular and monocular cues
Binocular cues
- Use both eyes
- Depth perception of close objects
- Retinal disparity and convergence
Monocular cues
- Use one eye
- Depth perception of far objects
- Size, overlap/position, linear perspective, texture, motion parallax
Retinal disparity
- Two eyes seeing objects from two different views
- Closer object = greater disparity
Convergence
Tendency of eyes to turn inward when an object is closer and vice versa
Gate control theory
- Pain perception
- Differentiates two types of nerve fibers in spinal cord
- “Gate” opens for pain signals (small unmyelinated) but closes for other sensory signals (large myelinated)
Two types of nerve fibers in spinal cord (gate control theory)
- Small unmyelinated - transmit most pain signals to brain
- Large myelinated - transmit other sensory signals to brain
Synesthesia
- Sensations in one modality spontaneously trigger sensations in another modality
- Most common = grapheme-color
- May be genetic, increased cross-activation and cross-connectivity in brain’s sensory areas
Grapheme-color synesthesia
Letters and numbers associated with colors
Psychophysics
Study of relationship between magnitude of physical stimuli and psychological sensations
Four psychophysics theories
- Weber’s Law
- Fechner’s Law
- Stevens’s Power Law
- Signal Detection Theory
Weber’s Law
- Just noticeable difference (JND) is a constant proportion regardless of object intensity
- Only applies to some stimuli and mid-range intensities
- Weight proportion = 2%
Fechner’s Law (Fechner-Weber Law)
- Logarithmic relationship (JND grows to increasingly greater degree with each increment in intensity)
- Only applies to some stimuli and better than Weber’s for extreme intensities
Stevens’s Power Law
- Exponential relationship, with differing exponents based on stimuli
- More accurate than Weber’s and Fechner’s laws
- Developed from research on method of magnitude estimation
Method of magnitude estimation
- Participants assigned numbers to stimuli based on sensations elicited
- Relationship between physical stimuli and sensation differs for different stimuli
Signal Detection Theory
- Perception (and accuracy) of a stimulus comes from both sensory and decision-making processes
- Decision-making always uncertain due to background noise (other neural activity, fatigue, distractions)
- Decision-making affected by sensitivity and decision criterion
Sensitivity
Perceiver’s ability to differentiate between stimulus and background noise
Decision criterion (decision bias, response bias)
Perceiver’s willingness or tendency to say a stimulus is present in ambiguous situations
Signal Detection Theory research
- Participants presented with weak or absent stimulus in a noisy background and then asked whether they detect signal or not
- d-prime = estimate of sensitivity
- ROC curve = how often hits and false alarms may occur for different levels of sensitivity, impact of changes in decision criterion
Four possible outcomes in Signal Detection Theory experiments
- Hit = says present (correct)
- False alarm = says present (incorrect)
- Miss = says not present (incorrect)
- Correct rejection = says not present (correct)
