Topic 1 - Introduction to Perception Flashcards
The Perceptual Process
The journey from stimuli to responses in seven steps
- Distal and Proximal Stimuli
- Receptor Processes
- Neural Processing
- Behavioural Response
Sensation vs Perception
Sensation involves simple processes that occur at the beginning of a sensory system, while perception is identified with complex processes that involve higher-order mechanisms
Distal and Proximal Stimuli (Step 1 and 2)
Distal Stimulus - a distant stimulus, light reflected from the stimulus reaching the visual receptors
Proximal Stimulus - the image on the retina caused by light reflections
Principle of transformation
stimuli and responses created by stimuli are transformed between the distal stimulus and perception
Principle of representation
everything a person perceives is based not on direct contact with stimuli but on representations of stimuli that are formed on the receptors
Receptor Processes (Step 3)
- Sensory Receptors
- Visual Pigment
- Transduction
Transduction
Step 3
transformation of one form of energy to another form (light energy to electrical energy in this case)
Sensory Receptors
Step 3
Cells specialised to respond to environmental energy
Visual Pigment
Step 3
Visual pigment - light-sensitive chemical in visual receptors causing them to transform light energy into electrical energy
Neural Processing (Step 4)
Changes in signals that occur as they are transmitted through a maze of neurons
Behavioural Response (Steps 5-7)
Electrical signals are transformed into conscious experience
A person perceives (step 5) and then recognises (step 6) and then takes action (step 7)
Bottom-up processing
AKA data-based processing
Based on stimuli reaching the receptors
Top-down processing
AKA knowledge-based processing
Based on existing knowledge
(The Perceptual Process)
Psychophysical Approach
The stimulus-perception relationship
- relates stimuli to behaviour responses (steps 1-2 and 5-7)
(The Perceptual Process)
Physiological Approach 1
Stimulus-physiological
Focuses on the relationship between stimuli and physiological response (steps 1-2 and 3-4)
(The Perceptual Process)
Physiological Approach 2
Physiology-perception
Focuses on the relationship between physiological responses and behavioural responses (steps 3-4 and 5-7)
Thresholds
measure the limits of sensory systems
Absolute threshold
the smallest stimulus level that can be detected
Difference threshold
smallest difference between two stimuli that can be detected
- also known as Limen
Method of limits
stimuli is presented in different intensities in either ascending order or descending order
eg. a hearing test where you respond when you first hear the sound, which is presented in increasing volume
Method of adjustment
stimulus intensity is adjusted until observer hears it
- repeated trials are averaged for result
Method of constant stimuli
Five to nine stimuli are present in a random order
Weber’s Law
the size of just noticeable difference is proportional to the original stimulus value
DL / S = K
Magnitude Estimation
Experimenter first gives a standard stimulus and assigns it a value. Observer is asked to give difference values to stimuli of varying intensity
Response compression
Magnitude Estimation
As intensity of stimuli increases, perceived magnitude increases more slowly than intensity
Response expansion
Magnitude Estimation
As intensity of stimuli increases, perceived magnitude increase more quickly than intensity
Action Potential
Na+ flows into fibre and makes neuron more positive
K+ flows out and makes neuron more negative
Na+ is pumped out and returns it to a normal level
Propagated response - once triggered, it travels all the way down axon without decreasing in size
Increases in rate in response to increased stimulus intensity
Refractory period of 1mm - upper rate is 500-800 impulses per second
Spontaneous activity
action potentials in the absence of stimuli
Neurotrasmitters
Released by presynaptic neuron from synaptic vesicles, received by postsynaptic neuron on receptor site
Triggers voltage change in postsynaptic neuron
Excitatory Response
When a neuron become more positive, more likely chance of action potential, increased firing rate
(Depolarization)
Depolarization
An excitatory response
Inhibitory response
When a neuron becomes more negative, less likely chance of action potential, decreased firing rate
(hyperpolarization)
Hyperpolarization
An inhibitory response
Neural circuits
interconnected groups of neurons - connected by excitatory and inhibitory synapses
Convergence
when a number of neurons synapse onto a single neuron
Simple circuit
No convergence and only excitatory inputs - only indicates a single spot of stimulation
Convergent circuit (excitatory)
input from each receptor summates into the next neuron in the circuit
- increases size of single neurons response
Convergent circuit (excitatory and inhibitory)
inputs summate to determine outcome
- weak response for single inputs and long stimuli
- maximum firing rate for medium length stimuli
Receptive field
area of receptors that affect firing rate of a neuron
- measured by using an electrode
Output of receptive field
- Highest response when excitatory area is stimulated
- Lowest response when inhibitory area is stimulated
- Intermediate responses when both areas are stimulated
Center and surround areas of receptive fields
- Excitatory-center-inhibitory-surround
- Inhibitory-center-excitatory-surround
Light focusing on retina
Cornea - refracts light - the outside curved surface
Lens - focuses light onto the retina
Blind spot
Occurs where the optic nerve passes through surface of retina, so there are no photoreceptors
- Brain fills in the missing information
Convergence (in the retina)
Rods have greater convergence than cones - results in summation in inputs of many rods into ganglion cells increasing likelihood of response (therefore more sensitive to light, cannot distinguish detail)
All-cone foveal vision results in high visual acuity - less convergence means attention to detail, but needs more light to respond
Rods, Cones and Ganglion cells (in the retina)
- 126 million rods and cones converge into 1 million ganglion cells
- Average of 120 rods to 1 ganglion cell, 6 cones to one ganglion cell
Lateral inhibition
inhibition that is transmitted across the retina
Lateral inhibition in Limulus
Hartline research - a decrease in firing from one receptor as three nearby receptors are also exposed to light
Phenomenological report
Describing what you see
Light perception Phenomena
- Hermann Grid
- Mach Bands
- Simultaneous Contrast
- Hermann Grid - seeing black dots at white intersections
- Receptors responding to corridors send inhibiting signals to receptor at intersection - causes a reduced response, hence grey
- Mach Bands - seeing borders more sharply (as different colours)
- Simultaneous Contrast - seeing areas of different brightness due to adjacent areas
(see notes for images)
