Readings

• What is the main topic of Week 4 in the study material?

  Illusions of colour perception and deficiencies of colour vision
• What is often referred to as instances of colour blindness?


  Deficiencies of colour vision
• Who provided a definition of illusory perception in 2005?


  1. H. Day
• What does an illusory perception refer to?


  A consistent and persistent discrepancy between the perceived and real physical properties of a stimulus
• What are the two characteristics of illusions as defined in the study material?

  Illusions are consistent and persistent
• Why does the definition of illusion have shortcomings when applied to colour?


  Because colour is a sensation and not a physical property
• What are the three basic shortcomings of Day's definition of illusion?


  1. Not every discrepancy is an illusion; some are absent from experience.
  2. Some discrepancies are due to optical effects, not perception.
  3. Visual representations like photographs are not considered illusions if the viewer is not deceived.
• What is the revised definition of a colour illusion?


  A colour illusion is when the perceived colour of a surface does not correctly represent its spectral reflectance function
• How does the visual system misrepresent reality in colour illusions?


  By not correctly representing the spectral reflectance of a surface
• What happens to the perceived colours of the squares when viewed without the rest of the picture?


  They appear gray
• What is the role of the visual system in colour perception?


  To extract information about spectral reflectances from reflected light
• What does the visual system need to discount the contribution of the illuminant spectrum?


  An estimate of the illuminant spectrum
• What is the gray world theory of colour constancy?


  • A theory that suggests the visual system estimates the illuminant spectrum.
  • It helps in discounting the contribution of the illumination to perceive true surface colours.
• Why do colour illusions occur according to the study material?


  They occur due to the processes that extract surface spectral reflectance information from images
• What happens to the illusory colours when the whole cube and its background are present?


  The illusory colours are perceived
• What is the spectral reflectance function of a surface that appears red?


  More reflective at long wavelengths than at medium or short wavelengths
• How does the spectral reflectance function of a surface that appears yellow differ from that of a red surface?


  It is more reflective on the long-side of the middle of the range than at either end
• What does the spectral reflectance function of a surface that appears blue look like?


  More reflective at the short end of the range than elsewhere
• What are the characteristics of the spectral reflectance functions for different colours?


  • Red: Reflective at long wavelengths.
  • Yellow: Reflective on the long-side of the middle range.
  • Blue: Reflective at short wavelengths.
• What is the relationship between the perceived colours of the squares and their actual spectral reflectance?


  The perceived colours misrepresent the actual spectral reflectance, which is gray
• Why do we not consider the motion seen in movies as an illusion?


  Because we are not deceived; we know it is just a sequence of still pictures
• What is the visual system trying to solve in colour perception?


  The problem of extracting information about spectral reflectances from reflected light
• What happens to the perceived colours of the squares when viewed in isolation?


  They appear gray
• How does the visual system estimate the illuminant spectrum?


  By using information from a large number of different surfaces
• What is the significance of the flat reflectance function in relation to colour perception?


  It indicates that the surface should look achromatic, or gray
• What is the visual experience when looking at the blue and yellow squares on the cubes?


  They appear to be blue and yellow, but they are actually gray
• Why is it important to understand the processes involved in colour perception?


  To comprehend how colour illusions occur and how we perceive reality
• What is the role of the processes involved in detecting and processing sensory stimulation?


  They determine the colour of each individual surface or surface patch
• How does the visual system's misrepresentation of reality relate to the concept of colour illusions?


  It shows how the perceived colour does not match the actual spectral reflectance
• What is the main focus of the lectures in Week 4?

  Illusions of colour perception and deficiencies of colour vision
• What is the significance of the distinction between perceived and real properties in illusions?


  It helps to clarify what constitutes an illusion
• How does the definition of illusion improve when considering the sensory percept and distal stimulus?


  It better accounts for colour illusions and other sensory experiences
• Why are discrepancies that are not surprising typically not classified as illusions?


  Because they do not deceive the observer regarding the true nature of what they are looking at
• What is the relationship between the perceived colour of a surface and its spectral reflectance in a colour illusion?


  The perceived colour does not correctly represent the spectral reflectance
• How does the visual system's processing of sensory stimulation relate to colour perception?


  It involves detecting and processing the properties of stimuli to determine colour
• What is the significance of the examples provided in the lecture slides regarding illusions?


  They illustrate the principles of colour perception and the nature of illusions
• Why is it important to recognize the difference between perceived and actual properties in colour perception?


  It helps in understanding how illusions can misrepresent reality
• What is the main conclusion regarding colour illusions in the study material?


  Colour illusions misrepresent the actual spectral reflectance of surfaces
• How does the visual system's estimation of the illuminant spectrum affect colour perception?


  It allows the visual system to discount the contribution of the illumination
• What is the role of the processes involved in extracting surface spectral reflectance information?


  They help determine the perceived colour of surfaces based on the reflected light