Introduction Flashcards
What is the goal of perception
To inform us about the properties of the environment that are important for our survival
We will not be here if peripheral system did not work
How is the goal of perception achieved?
Using information from our senses our perceptual system creates a model of the environment in our minds
Diagram of senses part of perception
“Create model of our environment”
Important note on model:
To appreciate what “sensations” and “perceptions” actually are, it is crucial to appreciate that this reconstructed representation or internal “model” of our environment is not simply a replica of our surrounding physical environment.
Let me try and convince you that your perceptions are not simply a copy of the external world…
e.g DOES NOT WORK BY TAKING PHONE AND TAKING PICTURE AND immediately goes in our mind
It is an ACTIVE PROCESS
Aims of perception
- Some objects or stimuli that you see (i.e perceive in isolation may appear differently in the presence of other stimuli)
- We sometimes see “things” that are not there
- And sometimes we can even fail to see “things” that are in fact out there…
Aim of perception one explained
e.g if you change position relevant to other stimuli appearance will change
What we perceive also depends on what else is out there:- contextual effects modify the appearance of objects (e.g. perceived brightness of an object or perceived orientation of lines).
Aim of perception two explained
- Such cases indicate that the process of building an internal model of our environment, namely of forming Perceptions, does rely on some stored knowledge of the physical properties of objects in our environment…
- For instance, if I cannot see circular sections of the underlying objects then there must be an opaque (white, in this case) circle above them…
- We may perceive “things” that are not there…(e.g. illusory dots, illusory motion or size constancy effects)
Aim of perception three explained
And sometimes we fail to see “things” which are in fact there…(e.g. change blindness).
Conclusion of perception
Perception is not a simple replication of our physical environment.
Diagram of perceptual knowledge
Figure 1.1 The perceptual process. These seven steps, plus “knowledge” inside the person’s brain, summarize the major events that occur between the time a person looks at the stimulus in the environment (the tree in this example) and perceives the tree,
recognizes it, and takes action toward it.
Explain this perceptual process in the diagram below:
- Stimulus in environment e.g tree
- Light is reflected on object and eye will focus on forming an image at the back of the eye
- Sensory organ of eye - receptor processes
- Neural processes towards visual pathway
- Perceptions are sometimes affected by stored knowledge
- What we perceive is function of past experience
Explain this
- Figure 1.6 Steps 5–7 of the perceptual process. The behavioral responses: perception, recognition, and action.
Where does perception occur?
In the brain
What are brains made out of?
(many) neurons that communicate with each other using electrical signals - more on that process in the next lectures.
Why is it a problem that electrical signals is the only language that the brain understands?
- Language that neurons communicate each other with
- It is a “problem” because the stimuli that arrive at our different senses are not electrical signals:
Example of why is it a problem that brain only communicate with electrical signals?
e.g
organs respond to different stimuli at senses are not electrical signals
- Eye – Light (electromagnetic radiation)
- Ear – Sound (air pressure)
- Vestibular system – Head movements (mechanical energy)
- Tongue – Taste (chemical / molecular shape)
- Nose – Odour (chemical / molecular shape)
- Skin – Touch, Temperature & Pain (Mechanical, thermal & chemical energies)
What is the solution that our brain can only process electrical signals?
Transduction
What is definition of transduction?
the process by which individual sense organs convert (or transduce) energy from any environmental events into neural activity.
Transduction is a conversion
How does transduction covert energy from enviro into neural activity?
Each of our sense organs (eyes, ear, nose tongue etc.) contain specialised receptors that translate the energy from corresponding stimuli into neural activity which our brain can then process.
e.g each sense organ have a different repecetor cell that is specialised
so take energy and make an electrical signal to the brain
Example of transduction in perceptual process
- E.G
- IN this case visual system the light will stimulate photoreceptor and output is electrical signals that could be processed into perceptual system
What are the two methods that get the electrical signals (just converted from transduction) into the brain?
- Transmission
- Processing
What is transmission?
carries the signals from the receptors to the brain and around the brain.
Also around the brain region to another to make a decision
What is processing?
Example of transmission, transduction and processing
Light
Figure 1.3 (a) Transduction occurs when the receptors create electrical energy in response to the light. (b) Tranmission occurs as one neuron activates the next one. (c) This electrical energy is processed through networks of neurons.
- Processing is unique as it makes our perceptual systems what they are
Example of transmission
- Comparison of signal transmission by cell-phone and the nervous system. (a) Cell phone #1 sends an electrical signal that stands for “hello.” The signal that reaches cell phone #2 is the same as the signal sent from cell phone #1.
Example of processing
The nervous system sends electrical signals that stand for the moth. The nervous system processes these electrical signals, so the signal responsible for perceiving the moth is different than the original signal sent from the eye.
Diagram of knowledge top down processing
Two interacting processes in perception
- Bottom -up processing
- Top down processing
What is bottom up processing?
Processing based on incoming stimuli from the environment
Also called data-based processing
This is where flow of information from the environment through the sensory system towards the brain
What is top down processing?
Processing based on the perceiver’s previous knowledge (cognitive factors)
Also called knowledge-based processing
Means from the brain down towards lower areas of the brain
based on stored knowledge
Example of bottom down processing and top down processing working together
explain
Incoming data from the outside towatds the brain towards sensory organ
incoming data : bottom up
recognising moth: top down
In this example, (a) the image of the moth on Ellen’s retina initiates bottom-up processing; and (b) her prior knowledge of moths contributes to top-down processing.
Another example of top down processing
Three approaches to study of perception
- Psychophysical approach (PP)
- Physiological approach (PH1)
- Physiological approach (PH2)
Three approaches to study of perception
Are they related?
These stages are interrelated and inform one another; we will consider several examples from each approach throughout this course.
What is Psychophysical approach? (PP)
the stimulus-perception relationship
You study the relationship between your perceptions as a function of changing physical properties
e,g changing length,colour, temperature of objects
What is Physiological approach (PH1) ?
the stimulus-physiology relationship
e.g Recording the activity of a visual neurons you go and record the electricity as a function of systematically manipulating stimuli in outside world gives insight how neurons process info
What is Physiological approach (PH2)?
the physiology and perception relationship
using EEGs or fMRI
Examples of approaches to study perception
explain
(a) The psychophysical relationship (PP) between stimulus and perception: Two colored patches are judged to be different. (b) The physiological relationship (PH1) between the stimulus and the physiological response: A light generates a neural response in the cat’s cortex. (c) The physiological relationship (PH2) between the physiological response and perception. A person’s brain activity is monitored as a person indicates what he is seeing.
Example of psychophysical experiment
(a) A reaction time experiment in which the subject was told to look at the + sign, but pay attention to the location at A, and to push a button as quickly as possible when a dark target flashes anywhere on the display.
(b) Reaction times in milliseconds, which indicates that reaction time was faster when the target was flashed at A, where the subject was attending, than when it was flashed at B, where the subject was not attending. (Data from Egly et al., 1994)
Human factor psychology task
Task: use your data from your Simple Reaction Time experiment to aid the design and implementation of a Collison waring system for a car.
You will have access to data from the car radar that constantly measures and monitors the distance to the car in front of you.
Your task is to advise the engineering team at what measured distance they must flash the
“You must break” waring signal to the driver before it is too late to break…
70 MPH = 112.654 Km/hour or = 31.3 metres/sec
or = 0.0313 metres/msec. [1000 milliseconds = 1 sec.]
Airing on the safe side of your results, we should use the higher average Reaction Time value of 300 msec.
300 (msec Reaction Time) x 0.0313 (metres covered every msec @70MPH) = 9.39 meters.
Thus, flashing a warning light at any distance below this value will be too late for the driver to react to…
Difference between sensation and perception
The sensation is identified as involving simple elementary processes that occur right at the beginning of a sensory system
e.g when light stimulates the receptors in the eye
Perception is identified with complex processes that involve higher-order mechanism such as interpretation and memory that involve activity in the brain
Between steps 1 and 2 is distal and proximal stimuli
Distal stimulus at the distance
distance something out in envnrioment
Person’s perception of the tree is based not on the tree getting into his eye but the light reflected from the tree and reaching the visual receptors.
proximal stimulus is then created image created on the retina
Step 3 in more information
- Sensory receptor specialised to respond to environmental energy, with each sensory system’s receptor specialised to respond to specific type of energy
Step 4 more detail
neural processing
This is once transduction occurs
represented in electrical signals
What is the oblique effect?
People see vertical or horizontal lines better than lines orientated obliquely (any orientation other than vertical or horizontal)
