Unit 3

• Attention


  Conscious awareness
• Sensation


  Reception of external stimuli by sensory systems

  
• Perception


  Interpretation of external signals by the brain and giving them meaning

  
• The brain constructs perceptions from sensory information

  
• Sensation and perception both begin with the basic process of attention

  
• Attention


  Focusing of awareness, selectively filtering out uninteresting or unimportant noise from surroundings
• Psychophysics


  Study of how the mind interprets the physical properties of stimuli, looks at relationships between sensory information and perception, measures limits (thresholds) of awareness of sensory systems

  
• Absolute threshold


  Minimum intensity of stimulus that can be detected at least 50% of the time, under ideal circumstances
• Absolute thresholds of the five senses

  • A candle flame seen at 48 kilometers on a clear night
  • A teaspoon of sugar in 7.5 liters of water
  • A drop of perfume diffused into the entire volume of air in a six-room apartment
  • The tick of a wristwatch under quiet conditions at 6 meters
  • The wing of a fly falling on you from a distance of one centimeter
• Signal detection theory


  Our ability to detect presence of a stimulus is affected by more than just intensity of that stimulus, e.g. our motivations, experiences, and level of attention

  
• Possible outcomes in signal detection

  • Hit
  • False alarm
  • Miss
  • Correct rejection
• Just Noticeable Difference (JND)


  Minimum change in the intensity of a stimulus that can be detected 50% of the time, smallest detectable difference between two stimuli

  
• Weber's Law


  As stimuli get larger, differences must also become larger to be detected, the smaller/weaker the stimuli, the easier it is to detect small differences between them and vice versa
• Subliminal perception


  When the intensity of a stimulus is below the participant's absolute threshold and the participant is not consciously aware of the stimulus

  
• Vast majority of studies don't support the existence of extrasensory perception (ESP) or psi
• Differences in perception between men and women

  • Women: Better at discriminating objects, naming colours, processing facial expressions, perceiving colours, preferring warm colours, preferring dolls
  • Men: Better at processing moving objects, spatial aspects of objects, relative positions of places, preferring trucks, avoiding pink
• Top-down perceptual processing


  Perception guided by past knowledge, experiences, beliefs, desires, and expectations, can fill in parts of stimulus missing from actual sensation

  
• Bottom-up perceptual processing


  Perception not guided by prior knowledge or expectations, properties of stimulus itself used to build perceptions

  
• We probably use both top-down and bottom-up perceptual processes during a typical day
• Perceptual constancies


  Shape, size, brightness, and color constancy - the brain knows that just because something appears to change, does not mean that it actually does
• Binocular depth cues


  Depth perception based on information from both eyes, using retinal disparity
• Monocular depth cues


  Depth perception using one eye
• Gestalt principles


  Proximity, similarity, continuation, closure - principles that describe how we organize visual information
• Feature detection theory


  Theory that proposes we have specialized cells, called feature detectors, in the visual cortex that fire only when they receive input indicating a particular shape, colour, angle, or other visual feature
• Evidence suggests other areas of the brain may be organized to further process certain complex stimuli, e.g. the fusiform face area that processes faces
• Perceptual illusions


  • The Moon Illusion
  • The Ponzo Illusion
  • The Müller-Lyer Illusion
• Errors due to top-down processing

  Misperceptions caused by quickly making sense of information based on prior knowledge and expectations
• Errors due to perceptual constancy can cause tricks of the brain, like the Moon, Ponzo, and Müller-Lyer illusions
• People who live in "carpentered" environments with many rectangular structures tend to experience the Müller-Lyer illusion to a greater degree than those in "non-carpentered" environments