9 Flashcards
Sensation
The process by which the sense organs gather information about the environment and transmit the information to the brain for initial processing
Perception
The process by which the brain selects, organises and interprets sensations
3 broad principles S&P
- There is no one-to-one correspondence between physical and psychological reality; measuring this is the realm of psychophysics.
- Sensation and perception are active processes.
- Sensation and perception are adaptive (facilitation of survival and reproduction).
Features common to all sensory systems (1 & 2)
- Each sensory system has sensory receptors that:
- Detect physical energy (e.g., light waves)
- Translate physical stimulation into neural signals (transduction) - Each sensory system requires a minimum amount of energy to activate the system (threshold).
All senses have threshold below which a person does not sense anything despite external stimulation.
Features common to all sensory systems (3, 4 & 5)
- Sensation requires constant decision making
- Sensing the world requires the ability to detect
changes in stimulation. - Efficient sensory processing requires “turning down the volume” or suppressing redundant information
Absolute threshold
Sensory systems require a minimum amount of energy for activation.
Thresholds vary from person to person and situation to situation. Why? “Noise”!
• External noise
• Internal noise: random firing of neurons
• Internal noise: psychological factors such as expectation, motivation, stress, fatigue
Signal detection theory
making a decision about the presence or absence of a signal within the background noise due to
Initial sensory process
Decision process
Initial sensory process
the observer’s sensitivity to the stimulus
Decision process
the observer’s response bias (readiness to report detecting a stimulus when not certain)
Difference thresholds
The lowest level of stimulation required to sense that a change in stimulation has occurred.
Just noticeable difference (JND)
Weber’s law
Fechner’s law
Weber’s law
Regardless of the magnitude of two stimuli, the second must differ by a constant proportion from the first to be perceived as different.
Fechner’s law
The magnitude of a stimulus grows logarithmically as the subjective experience of intensity grows arithmetically.
Steven’s power law
As the perceived intensity of a stimulus grows arithmetically, the actual magnitude of the stimulus grows exponentially (squared, cubed, etc.)
Vision transduction
- Sensation requires converting energy in the world into neural signals.
- Specialized cells known as sensory receptors transform energy into neural impulses that can be interpreted by the brain.
- Transduction: the process of converting physical energy or stimulus information into neural impulses.
Retina
At the back of the eye, has photoreceptors (rods and cones) that traduce light into electrochemical signals (action potentials) when struck by light waves
Pupillary response
Pupil dilates or contracts:
- To changes in ambient lighting
- Emotion, motivation, arousal
Expansion of pupil is relatively slow however contraction is very quick
As pupil dilates, more light and therefore information is let in
Rods
Lower activation threshold, more sensitive so less light to activate
Cannot distinguish colour, not sensitive to the wavelength: linked to seeing in the dark however not colour
Located majority in the periphery: when star gazing look to the side of the star to line up the light with the side of your eye (where the rods are located)
Activated in between blue and green cones (450~600)
Cones
Higher activation threshold, less sensitive for light so require more photons fro activation
Located majority in the centre of the retina called the fovea
Responsible for detailed vision - why you cannot read in low light
Respond to wavelength therefore give us the ability to see colour
Cones=Colour=Centre
Response to short wavelengths
Blue cones as shorter wavelengths produce the colour blue
Activated before 400nm until around 500nm
Response to middle wavelengths
Green cones as medium wavelengths produce the colour green
Activated at around 475nm until around 650nm
Response to long wavelengths
Red cones as longer wavelengths produce the colour red
Activated at around 550nm to around 725nm
The law of common fate states
Things that are moving in the same direction will be grouped together
For example, dots moving in the same direction are perceived as a group of dots moving together.
Retinal disparity
differences between the two retinal images of the same scene – is a binocular depth cue
The greater the disparity of an object, the further away the object is perceived to be. Linear perspective, interposition and familiar size are all examples of monocular depth cues
Top down processes
include expectations, motivations and knowledge
Bottom up processes
include sensations, which are based on physical data from the environment
Combination of top down and bottom up processes
The combined influence of top-down and bottom-up processes on perception are evident in illusions, where the physical properties of the stimulus do not match the perceived properties of the stimulus.
