and
"Just Noticeable Difference"
Sensation - is the detection of physical energy emitted or reflected by physical objects
Perception - The set of processes that organize and interpret sensory impulses. Allows us to identify objects.
Necker Cube Allows for the perception of two different cubes.
The source of our perception: Sensory experience
Johannes Muller's (1826) Doctrine of Specific Nerve Energies suggests that specific types of sensation accompany certain sensory nerves.
E.g., any type of stimulation (light or mechanical) of the visual nerves will lead to sensation of light.
Synesthesia - "joining of the
senses"
E.g., tasting shapes, hearing
colours)
Links:
Synesthete
2 Cytowic
Synesthesia Test TED
Gustav Theodor Fechner (1801-1887):
Psychophysics (1860)
"Two-point threshold"
and
"Just Noticeable Difference"
Psychophysics: An exact science to establish mathematical relationships between physical and psychic magnitudes
Absolute Threshold:
Limen of minimal intensity for conscious sensation. It is the point at
which correct identification of stimuli occurs at 50% of trials. (e.g, varying
levels of brightness-candle,
loudness-watch, pressure-bee wing,
smell-perfume)
Difference Threshold : Change in intensity for a JND - smallest difference that is noticeable.
Weber's Law - size of change needed to be perceived: varies against background level to produce a constant proportion (JND) (just noticeable difference).
jnd = ~2% weight or brightness,10% loudness
Weber-Fechner function : S = K log R
Subliminal Perception studies have also been done to consider whether or not we can influenced but (hidden messages) in photos, films, and sounds. Greenwald (1991, 1992) has shown that no such effect exists. see also Auditory messages (Vokey & Read, 1985)
However, Priming does have an impact on our perception (likely due to emotional content), which is related to the mere exposure effect- when we tend to prefer things that we have had brief (multiple) exposures to over those that are novel.
Sensory Adaptation - The reduction of sensory responsiveness when a stimulus is unchanging or repetitive.
Rarely adapt to extreme stimuli or to visual ones - ( eyes move and "re-stimulate" different parts of the retina).
Sensory deprivation - the absence of 'normal' levels of sensory stimulation. -Participants in a study felt "edgy" within a few hours (many quitting the first day), many reported hallucinations. Room
-Today many people pay for "time out".
Sensory Overload - too much noise & excitement can be discomforting too -> fatigue, mental confusion (STRESS)
-[sometimes used for 'brainwashing'].
Selective Attention - the focusing of attention on selected aspects of environment and the "blocking" of others.
(e.g., -"Cocktail Party Phenomenon
" - lots of noise, ... but you recognise your name being said in spite of
all the noise.
Have partial awareness to all, but only some get more full
awareness.
Vision
Light: part of the EMR spectrum that extends from short ultraviolet (x-rays, gamma cosmic) through long infra-red (microwaves, TV, Radio).
1) Hue - is related to wave length of light.
2) Brightness - or luminance is the amount of light emitted from or reflected by an object.
3) Saturation - the vividness or purity of colour; complexity of light waves (number of different wave lengths contained in a light source.
An Eye on the World
The structure and parts of the Eye
There is an uneven distribution of rods and cones throughout the eye.
Near and far sightedness is usually due to the shape of the lens or eye.
The visual path is such that both eyes project images to both hemispheres.
Cortical Feature Detectors
-
Hubel and Weisel 1981 Nobel Prize:
on Cats
Found that "
simple "
cells for single lines in one
orientation
or movement later found
complex & hypercomplex cells that fire only for complex stimuli "A"
Similar supercell clusters are present for other important 'objects' or sight eg: monkey faces
How We See Colours: Two major theories
1) Trichromatic (Young-Helmholtz) we have three separate mechanisms (types of cones) that code for certain wave lengths of light. blue , green, red.
2) Opponent-Process
theory Bi-polar and Ganglion cells in retina and thalamus - operate as opponent
process cells are excited by one colour (red
) and inhibited by its opposite colour (green
), or vice versa. Same for blue - yellow.
Sending a colour code to higher brain centres can't see red-green (except at the Possum Lodge)
Negative
After Images
- get a "rebound of the opposite colour
Colour Blindness - total insensitivity is rare, usually red-green deficient while yellow blue is less common.
Place theory tells us that the location on the basilar membrane is where we are stimulated to hear various frequencies (particularly the higher ones).
Frequency theory tells us that the rate of firing of auditory receptors gives us a sense of pitch or tone.
Loudness is experienced by the number of hair cells activated by a sound.
Like the visual cortex the auditory cortex is
organized very well,
here as a
tonotopic field
Pheromones: chemical signals - affect humans?
Also look over the sense of touch, we will look at Pain in the section of Perception
