Visual Perception Flashcards
What is sensation?
The bottom up process by which our senses like vision, hearing and smell, receive and relay outside stimuli. (PHYSIOLOGICAL) The three stages are: *Reception *Transduction *Transmission
What is perception?
The top down way our brains organise and interpret specific information and put it into context. (PHYSIOLOGICAL and PSYCHOLOGICAL) The three stages are: *Selection *Organisation *Interpretation
What is the absolute threshold of sensation?
The minimum stimulation needed to register a particular stimulus under ideal conditions fifty percent of the time.
What is the differential threshold?
The smallest difference in the amount of a given stimulus that a specific sense can detect.
Rods
- Black and white vision
- Peripheral vision
- They have low visual acquity (can’t register detail)
- Concentrated at the edges of retina
Cones
- Concentrated in the middle of the retina (fovea)
- Responsible for vision of detail
- Responsible for colour vision and black and white vision in daytime
- Require high levels of light to enable them to respond
Reception
The collection of light by the eye and focusing it on the retina, which contains the photoreceptors (light-sensitive cells) called rods and cones.
Transduction
Conversion of electromagnetic energy (light energy) into electrochemical energy (or nerve mpulses) by photoreceptors (rods and cones).
Transmission
Transmission of neural impulses along the optic nerve to the primary visual cortex in the back of the brain.
Selection
Selection of features of a stimulus by specialised neurons in the visual cortex called feature detectors.
Organisation
Visual information reaching the brain’s visual cortex is reorganized using perceptual principles (perceptual constancies, Gestalt principles, depth cues).
Interpretation
The brain’s temporal lobes identify the object by comparing incoming information already stored in memory (perceptual set), and the parietal lobes assist in judging where the object is in space.
Monocular Depth Cue
Information about depth available in just one eye’s view.
Binocular Depth Cue
Requires both eyes to work together to provide information about depth and distance.
What are the two types of monocular depth cues?
Accommodation
Pictorial Depth Cues
Types of pictorial depth cues?
Linear Perspective
Interposition (overlap)
Texture Gradients
Relative Size
Height in the visual field
Linear Perspective
Parallel lines that appear to converge as they extend towards an imaginary point.
Interposition
When one object partially blocks another; the partially blocked object is perceived as further away.
Texture Gradient
Gradual reduction of detail that occurs in a surface as it recedes into the distance.
Height in the visual field
Objects that are closer to the horizon are perceived as further away.
What is perceptual constancy and what is it useful for?
- Recognising familiar objects as having standard shape, size, colour, or location - regardless of changes in the angle of perspective, distance, or lighting.
- Helps us identify objects under various conditions.
Types of perceptual constancies?
Size constancy
Shape constancy
Brightness constancy
Orientation constancy
Size constancy
Recognising that an object’s actual size remains the same even though it changes on your retina.
Shape constancy
Regardless of angle, we tend to perceive an object as maintaining its shape.
Brightness constancy
Tendency to perceive an object as maintaining its level of brightness in relation to its surroundings despite changes in the amount of light.
Orientation constancy
When you perceive the object as being the same regardless of the orientation.
What is the perceptual set?
- Stresses the idea of perception as an active process involving selection, organisation (inference) and interpretation.
- Stimuli is perceived in a specific way for each individual
What does the perceptual set include?
Previous experience
Context
Motivation
Emotion
Previous experience in perceptual set refers to?
Subjective interpretations based on an individual’s intellectual capacity, personality traits, upbringing, attitudes & values.
Context in perceptual set refers to?
- The environment in which a stimulus is observed.
* The same behaviour or event may be perceived differently depending on the circumstance.
Motivation in perceptual set refers to?
We often see what we want to see - ‘FOOD ADHEAD’ could be seen as ‘FUEL AHEAD’. (or other way around if you’re hungry)
Emotion in perceptual set refers to?
Can interpret things we see with a valence towards the emotion we are feeling.
What is distortion of perception?
Otherwise known as visual illusions.
Mistaken perceptions of a visual stimuli.
It’s the brain that causes the effect, not the eye!
Behavioural perspective in distortion of perception?
We experience the illusion because it contradicts what we have previously learnt and experienced.
‘The Carpentered World Hypothesis’
We are deceived by the illusion’s similarity to architectural features we are familiar with in the real 3D world.
Biological Perspective in distortion of perception?
Role played by our eyes, nervous system and brain when we view the illusion. i.e. failure to properly perceive the image.
Socio-cultural perspective in distortion of perception?
A study with Zambian participants who lived in urban areas showed that they were more likely to perceive illusion than those living in rural areas.
Cognitive perspective in distortion of perception?
*Suggests that the illusion may be due to using inappropriate mental strategies when interpreting the incoming visual information.
i.e. assuming that a smaller line is further away than it actually is.
*Said to occur because we incorrectly use the principle
of size constancy.
Motion-after effect illusions
- The apparent motion of a stationary stimulus following the extended viewing of a continuously moving stimulus.
- Can apply to the sense of touch - pain, pressure and temperature.
Types of binocular depth cues?
Retinal disparity
Convergence
Retinal disparity
- The lateral separation between objects as seen by the left eye and the right eye.
- Each eye views a slightly different image of the same scene and the brain fuses the two images together and we observe a real 3D scene.
Convergence
Convergence refers to the fact that the closer an object, the more inward our eyes need to turn in order to focus. The farther our eyes converge, the closer an object appears to be.
What are photoreceptors and what stage of sensation are they involved in?
Light sensitive cells called rods and cones. Involved in transduction where they convert electromagnetic energy (light) into electrochemical nerve impulses.
What are feature detectors and in what stage of perception are they involved in?
Feature detectors are cells that individually respond to lines of a certain length, lines at a certain angle, or lines moving in a certain direction. Involved in selection, where they break up the image transmitted to the brain.
Where are feature detectors found?
In the optic nerve and the primary visual cortex.
The phi phenomenon
One still picture after another gives an impression of movement.
Figure-ground organisation
Figure and ground are separated by an imagined contour line; contour is ‘owned’ by the figure.
Camouflage
‘Figure-ground’ is used to blend the contour of the figure against the ground, making figure more difficult to see.
Closure
When an object is perceived as being a whole, despite it actually being incomplete.
Similarity
When the individual parts of a stimulus pattern are similar (ie size, shape or colour), we tend to group them as a meaningful ‘whole’- a single unit.
What is depth perception?
The ability to accurately judge 3D space and distance using cues in the environment.
Proximity
When the individual pars of a stimulus pattern are close to each other, we tend to group them as a single unit.
List the Gestalt principles of perception
- The Phi Phenomenon
- Figure-ground organisation
- Camouflage
- Closure
- Similarity
- Proximity
Why are depth cues vital to us?
We only have 2D images on our retina but need to judge depth and distance in the 3D world.
What are the types of depth cues?
- Monocular depth cues- accommodation, pictorial depth cues
* Binocular depth cues- retinal disparity, convergence
The Ponzo illusion
Upper line in diagram is perceived to be longer than bottom line due to depth cues of linear perspective and height in visual field.
What is a visual illusion?
A figure constructed so that perception will consistently differ from objective relity
What is the Ames Room illusion?
The Ames Room Illusion shows that we maintain shape constancy (of a room) at the expense of size constancy. While the room appears square-shaped from the viewer;s perspective, it actually has a trapezoidal shape. The illusion leads the viewer to believe that the two individuals are standing in the same depth of field, when in reality the subject is standing much closer.
Purpose of perceptual constancies?
Enables us to maintain a sable perception of a stimulus, although the image on the retina may change (ie in size or shape)
What is a motion after-effect illusion?
The apparent motion of a stationary stimulus (object) following the extended viewing of a continuously moving stimulus. The stationary stimulus appears to move in the opposite direction.
What is the Muller-Lyer Illusion?
Optical illusion in which a line with feather heads (inward pointing arrowheads) is perceived as being longer than an equal line with arrowheads, when they are of equal length in reality.
Accommodation
The process by which the ciliary muscles of the eye change the curvature of the lens to focus an image on the retina.
Lens
A transparent, convex structure behind the iris that changes shape to focus light into an image on the retina
Iris
A coloured, circular muscle inside the eyes that expands and contracts to change the size of the pupil
Cornea
A transparent, convex shaped membrane that protects the front part of the eye
Pupil
An adjustable opening in the centre of the eye’s iris through which light enters; appears as black
Ciliary muscle
Muscle involved in accommodation of eye.
Blind spot
The opening in the retina through which the optic nerve exits the brain (contains no rods and cones)
Optic nerve
nerve that connects the eye to the brain
Retina
Light sensitive membrane composed of a number of layers of specialised neurons at the back of the eye
Fovea
A small, cup shaped area in the middle of the retina containing only cones.
