Flashcards in TOPIC 5: SENSATION Deck (94)
encoding environment energy or chemicals in terms of neural signals.
organization and interpretation of neural signals.
the study of relation between physical quantities and physiological experience.
weakest stimulus detected 50% of the time.
hypnosis or hoax?
-- “subliminal” perceived up to 49% of the time.
-- what about stimuli never consciously perceived?
James Vicary (1957)
- reportedly showed 0.03 second messages repeatedly during a movie.
Murphy and Zajonc (1993)
will subliminal stimuli enter our awareness??
- presented Chinese characters preceded by subliminal faces.
- ratings of characters depended on facial expressions. (smiles=positive)
CBC show Close-Up to subliminal messages (1958)
- replicated study and no effect on behaviour .
difference threshold (just noticeable difference or JND)
smallest difference between two stimuli detected 50% of time.
JND increases as ..
JND increases as stimulus intensity increases.
Weber's Law (1834)
JND is a constant proportion of stimulus intensity.
how does our experience change as intensity changes?
example: are two identical light bulbs twice as bright as one?
sensory experience is proportional to the number of JNDs a stimulus is above threshold.
S = k loge (I )
S = sensory experience,
k = Weber fraction,
I = stimulus intensity
problems with Fechner's and Weber's law
- less accurate approaching absolute threshold
- less accurate with increase intensity
- observers response bias confound attempts to measure sensitivity, due to time of day, fatigue
Steven Power Law (1961)
uses magnitude estimation technique:
1) observer given standard stimulus, and certain value.
2) observer assigns values to other stimuli.
Steven Power Law Formula
S = aI^b
S = sensory experience
a = constant
I = stimulus intensity
b = exponent
evolutionary adaptive significance
• pain quickly becomes very aversive (b>1)
• accurate estimation of length and distance (b=1)
• large range of light intensities can be perceived (b<1)
Signal Detection Theory
uses catch trials; no stimulus presented 50% of the time.
- determines observers response bias
- applies statistical methods to separate sensitivity from confounding factors
- does not determine a threshold
- Transduction of photons (light energy) to neutral impulses
narrow slice of electromagnetic spectrum; exhibits properties of particle and wave characteristics .
Object in the world
pattern of energy impinging on receptors
How does travel through the eye ?
===> pupil (iris)
===> crystalline lens
lens changes its shape, which changes its focal length, keeping image focused on retina.
rods and cones (contain photochemical)
hole where optic nerve exits; no receptors; BLIND SPOT
for directed looking; contains only cones.
experience of sensation changes with prolonged exposure.