Lecture 3 - Perception Flashcards
What is perception?
Experience resulting from stimulation of the senses
A complex set of processes by which we organise, recognise and make sense of the sensations we receive from environmental stimuli
- changes based on added information
- an active processes similar to reasoning or problem solving
- occurs in conjunction with action
The perceptual system uses two types of information
- environmental energy stimulating the receptors
- knowledge and expectation the observers bring to the situation
Senses:
- sight
- hearing
- smell
- touch
- taste
- temperature
- balance
- Proprioception
- nociception
- vibration
- pressure
- vestibular sense (balance)
- interception (internal body signals such as hunger, fatigue etc)
Perceptual objects are not reflections
The perceptual object is an interpretation and reproduction of the distal object, rathe than a reflection
Is human perception special?
Other species ‘see’ things that are invisible to us
Unlike humans, most mammals, many birds and insects and fish can see ultraviolet light
- goldfish can see uv and infrared
- snakes can see temperature
Attempts to create artificial forms of perception (machines) have been met with limited success ad each time have had problems that could not be solved
Did you know humans have stripes?
Probably not, but pets might
Blaschko lines are unique human markings in our skin that are very similar to zebra stripes
They are in isle to our visual system by easy to identify for species that can see uv light
We can sometimes see the, under very strong UV light which suggests that animals that can see UV light might recognise us based on our stripe pattern
However some conditions (chimera, mosaic) can make Blaschko lines visible to the human eye
Why is it so hard for computers to copy human perception?
The inverse projection problem
Objects can be hidden or blurred
Viewpoint invariance
The inverse projection problem
The stimulus on the reports in the retina is ambiguous
We loom at a page of a book and know what it is because of our previous knowledge, but it is an ambiguous object if you didn’t know what it was
Task of determining the object for a particular image on the retina
Involves starting with the retinal Uk age then extending outwards to the source of that image
A page of a book could have been created by many different objects located at different distances
When we consider the fact that a 2D image on the retina can be created by a wide range of 3D images, we can see why the image is ambiguous and tat e need to figure out what it is
Humans can do this easily, however it is very hard and caused a lot of problems trying to programmes this into a computer
Objects can be hidden or blurred
Computers see via edges (contrast between neighbouring pixels)
They cannot interpolate missing parts
If an image is not shape, they cannot compute edges
People can often identify objects that are observed and there for incomplete or blurry, but cannot be computed into a computer
Viewpoint invariance
Objects look different from different viewpoints
Objects are often viewed from different angles - means objects are constantly changing in how they look depending on their angle
Humans are able to perceive these images the same way and as the same object, but computers struggle to do this
Approaches to understanding perception
Direct perception theories:
- bottom up processing
- perception comes from the stimuli in the environment
- parts are identified and put together and then recognition occurs
Constructive perception theories
- top-down processing
- processing originates in the brain, ‘top’ of the perceptual system
- people actively construct perception using information based on expectation
Bottom-up processing
Perception starts with the senses
Incoming raw data - light is reflected into our eye, onto our retina, from the object that we are looking at
Energy registering on receptors
Receptors then translate the environmental energy into neural signals that are transmitted, via the thalamus, into the cortical areas of the brain that will process and store it
Top-down processing
We need people’s knowledge, experience and expectations
Processing starts in the brain
Person’s knowledge, experience and expectations
We also need tiger attention towards specific stimuli
Percept5ion involves both top down and bottom up processing simultaneously
Bottom up vs top down - perception of pain
Pain occurs when receptors in the skin are stimulated
- direct pathways from skin to brain (direct at ways model)
This is a bottom-up process because it depends on stimulation of the receptors
Pan curs when receptors in the skin are stimulated
Pain is influence by what a person expects, how the person directs their attention an distracting stimuli present which is a top-down process
Top down processing in language
Top down processing influence our perception of language based on our individual experience with language
Speech segmentation - ability to tell when one word ends and another begins
Transitional possibilities - knowing which sound will likely follow another in a word
Helmholtz’s unconscious inference
Top-down theory to address visual ambiguity
Some perceptions are the result of unconscious assumptions we make about the environment
- we use our knowledge to inform our perceptions
We infer much of what we know about the world
Likelihood principle - we perceive the world in the way that is ‘most liely’ based on our past expeirnce
A big part of his theory was that all of this top-down processing from our knowledge and the principle of likelihood is that the process of perceiving what is most likely to have caused the image on the retina happens quickly and unconsciously and therefore results in perceptions that seem ‘automatic’
Perceptual organisation - Gestalt
Historic view from structuralism - perception involves adding up sensations - Gestalt’s work inspired a surge in what is now referred to as Gestalt psychology and formed a group of principle laws that explain the way we perceive things
New view - Gestalt principles
- the mind group patterns according to intrinsic laws of perceptual organisation based on knowledge about the world
Figure ground principle:
- there needs to be an object and its background
Good continuation:
- points that, when connected, result in straight or smoothly curving lines as seen as belonging together, and the ones tend to be seen in such a way as to follow the smoothest path
- also, objects that are overlapped by the other objects are perceived as continuing behind the overlapping object
- lines tend to be seen as following the smoothest path
- good continuation helps us perceive the rope as a single strand
Law of pragnaz:
- principle of simplicity or good figure
- every stimulus pattern is seen so the resulting structure is as simple as possible
- demonstrated with the Olympic rings
Principle of similarity:
- similar nothings appear grouped together
- if we are presented images of shapes and colours, we will group them these images into either columns and rows depending on which ones are similar to each other
Perception is determined by specific organising Principles, not just lights waves activating the retina
Perceptual organisation is a feature of the stimulus (bottom up)
Roles of experience is ,i or compared to these intrinsic ‘built in’ principles
Experience can influence perception but is not the key driver
