Seeing is Perceiveing

• What is sensation?

  The process of detecting & receiving stimuli from the environment
• What is sensation, in terms of visual perception?

  Describes the reception of light by rods & cones in the retina, which is converted to neural signals via transduction & transmitted to the brain via the optic nerve as APs
• What is perception?

  The processing (organisation & interpretation) of sensory information that occurs after information is transmitted to the brain
• What is perception in terms of visual perception?

  Enables us to recognise objects & events (percept)
• What is the process of visual sensation?

  Light from environment projected onto retina -> photoreceptors transform light into electrical impulses -> transmitted via optic nerve to visual cortex
• What is the process of visual perception?

  Information processing that combines neural signals with prior knowledge, expectations & beliefs to help us make sense of the world

  Facilitates the recognition & understanding of objects & scenes

  Active process -> allows us to recognise, locate & detct even with frequently changing stimuli

  Results in different experiecnes
• Give 3 processes of perception.

  Selection

  Organisation

  Interpretation
• What is selection, in terms of perception?

  External environment is too detailed to process everything we 'see', have to be selective

  Selection driven by attention & filters out irrelevant stimuli to avoid 'overload'

  Attend information relevant to current goals, or that has emotional significance

  Can be bottom-up or top-down
• What is inattentional blindness?

  Failure to perceive fully visible stimuli if not selected/attended to
• What is change blindness?

  Failure to perceive a substantial visual change
• What is bottom-up processing?

  Data-driven

  Processing starting with the information derived from the senses (e.g. colour, orientation, size)-> looking for clues (e.g. in letter shapes to 'decode' letters)
• What is top-down processing?

  Constrictivist

  Processing starting with pre-existing knowledge (e.g. experience, location, meaning)
• What is organisation, in terms of perception?

  Process of organising & grouping items together so we can perceive them 'as one'

  Tend to organise information into patterns based on certain prinicples

  Automatically make assumptions about simplest organisation
• What is Gestalt psychology?

  Translates to shape, form

  Study of how we perceive experiences

  Perception of the 'whole' is different to the sum of its parts in predictable ways
• What are the Gestlalt Principles (Laws of Perception)?

  Law of Prägnanz

  Figure-ground relationship

  Perceptual Grouping
• What is the Law of Prägnanz?

  What we see is the simplest & most stable interpretation of the elements

  Laws of Gestalt were based on this law

  E.g. seeing a dalmation, rather than lots of random dots

  
• What is figure-ground relationship?

  We distinguish between figures (subject of the image) and the ground (background)

  Draws attention to the figure

  Can be affected by how we interpret sensory information, therefore what we interpret as the 'figure' and the 'ground' can vary

  E.g. in image, are the faces or the 'candlestick' the figure

  
• What is interpretation, in terms of perceiving?

  A percept is not complete replication of visual world

  Interpreting information into meaningful experience (inc. colour, depth, distance)

  Information gathered from stimulus & surroounding cues

  Information can conflict
• Describe depth perception?

  Images form in retina in 2D

  Depth perception allows us to percieve images in 3D

  Use binocular & monocular clues

  Binocular (both eyes)

  • only helpful at short distances
  • retinal disparity (overlapping of views from eyes) & convergence

  Monocular (one eye)

  • use to judge gradient, relative size, position on the horizon
• The Visual Cliff

  Between 2-6 months babies develop ability to understanding depth

  Show anxiety & understanding of danger

  Innate & protective process

  
• What is perception set?

  The biases, experiences & expectations we bring to bear when interpreting a visual scene

  Can result in differing perception if same object/scene compared to what is actually there (visual illusions)
• What is perceptual bias?

  A predisposition to interpret a stimulus a certain way

  Influences by perceptual set (past experience, what we expect to see, motivation, emotion, individual differences)

  Perceptual bias can lead to perceptual error
• How can instruction & framing lead to perceptual bias?

  Instruction -> 'be cautious' can lead to increased false positives (e.g. NHS cancer screening)

  Framing -> of information can influence perception of risk & decision making
• How can motivation & emotion influence perceptual bias?

  We see what we are motivated/primed to see

  Emotions influence perception & interpretation of events
• How can expectation influence perceptual bias?

  People see what they expect to see

  Results in change blindness when our expectations for a scene block actual perception
• What is visual agnosia?

  Unable to know
• What is apperceptive agnosia?

  Cannot recognise by shape

  Cannot copy drawings
• What is associative agnosia?

  Can copy shapes

  Cannot associate meaning with shapes
• What is prosopagnosia?

  Inability to recognise faces only
• What is Capgras syndrome?

  Inability to recognise known people

  Belief that they have been replaced by an imposter
• What are the different types of perceptual grouping?

  Closure - see things as complete wholes rather than segmented parts

  Good continuity - more likely to perceive smooth continuous lines rather than abrupt changes

  Proximity - elements placed together are perceived to be part of the same object rather than separate ones

  Similarity - objects that look the same are perceived as being together