TOPIC 5: SENSATION Flashcards
sensation
encoding environment energy or chemicals in terms of neural signals.
Perception
organization and interpretation of neural signals.
Psychophysics
the study of relation between physical quantities and physiological experience.
Absolute threshold
weakest stimulus detected 50% of the time.
subliminal stimulation
hypnosis or hoax?
– “subliminal” perceived up to 49% of the time.
– what about stimulineverconsciously 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 showClose-Upto 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.
scaling
how does our experience change as intensity changes?
example: are two identical light bulbs twice as bright as one?
Fechner’s Law
sensory experience is proportional to the number of JNDs a stimulus is above threshold.
Fechners formula
S=kloge(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
Vision
- Transduction of photons (light energy) to neutral impulses
Visible light
narrow slice of electromagnetic spectrum; exhibits properties of particle and wave characteristics .
Distal Stimulus
Object in the world
Proximal Stimulus
pattern of energy impinging on receptors
How does travel through the eye ?
cornea
===> pupil (iris)
===> crystalline lens
===>retina
Accommodation
lens changes its shape, which changes its focal length, keeping image focused on retina.
Receptors
rods and cones (contain photochemical)
Optic disk
hole where optic nerve exits; no receptors; BLIND SPOT
Fovea
for directed looking; contains only cones.
Sensory Adaption
experience of sensation changes with prolonged exposure.
Dark Adaption
rods lose sensitivity in bright light; regenerate bleached photopigment in - 20 mins.
Trade Off
adaption may decrease sensitivity to unchanging stimuli, BUT allows perception of important environmental changes.
Retina
area on the retina that, in reaction to a stimulus, influences the firing of a neutron.
primary visual cortex
- Hubel and Wiesel recorded cats brains
- Located in the occipital lobe
- Simple cells
- complex cells
- hypercomplex
(end-stopped) cells - includes feature detectors
simple cells
triggered by pattern in receptive field, such as a bar of light with certain width, orientation, and location.
complex cells
also requiring motion in specific direction
hypercomplex cells
must also have particular length
or moving corners/angles
feature detectors
groups of neurons within the primary visual cortex are organized to receive and integrate sensor nerve impulses originating in specific regions of the retina.