Sensation and Perception

• Process of stimulation becoming sensation

  (1)stimulation

  (2)transduction

  (3)sensation

  (4)perception
• (1) Stimulation


  Everything up until the point that the stimulus reaches the eye
• (2) Transduction


  Physical stimulation is transduced by an eye, where info about the wavelenghs and intensity of the light is coded into neural signals
• (3) Sensation


  The neural messages travel to sensory cortex of the brain, where they become sensations of colour, brightness, form and movement
• (4) Perception


  Interpreting sensations by making connections with memories, expectations and motives in other parts of the brain
• Neural messages


  language of the nervous system

  The brain senses the world INDIRECTLY because the sense organs convert stimulation
• Sensory impressions involve 


  neural REPRESENTATIONS of stimuli
• Sensation definition 


  The process by which stimulation of a sensory receptor produces NEURAL IMPULSES that the brain interprets as a sound, image etc
• Sensation represents…


  the first series of steps in processing of incoming information
• Perception definition 


  A process that makes SENSORY patterns MEANINGFUL
• Bottom-up processing


  STIMULUS-DRIVEN;

  Taking sensory info and then assembling and integrating it
• Top-down processing


  CONCEPTUALLY DRIVEN;

  using models, ideas, and expectations to INTERPRET sensory info. Facilitates bottom-up processing
• Sensation features

  • immediate/fast
  • veridical (faithful/accurate)
  • initial step leading to perception
  • sensitivity
• Sensitivity


  All the senses operate in the SAME way, but each EXTRACTS different information and sends it to its own specialized processing region in the brain
• Properties of sensation 


  Absolute threshold, discrimination, Weber’s law
• Absolute threshold


  Minimum level of stimulus intensity required to detect a particular stimulus at least 50% of the time.

  The WEAKER this minimal intensity of the stimulus (lower threshold), the more sensitive we are - psychophysics
• Methods of measuring absolute threshold

  Method of limits, adaptive testing, method of constant stimuli
• Method of limits 


  Involves presenting a series of stimuli with varying intensities in ascending and descending order until the participant DETECTS or FAILS to detect the stimulus
• Ascending intensity


  This means the stimulus gradually increases in strength. For example, if you slowly turn up the volume on your music, the sound intensity is ascending.
• Descending intensity 


  This means the stimulus gradually decreases in strength. For example, if you slowly turn down the volume on your music, the sound intensity is descending.
• Adaptive testing


  Lowest intensity level at which we detect stimulus 50% of the time; varies between persons
• Method of constant stimuli

  Presenting a set of stimuli with varying intensities in a RANDOM order, and the participant is asked to detect whether they detect

  the stimulus or not. Done until 100times
• Discrimination 


  The ability ro differentiate between 2 stimuli that are presented at or near the threshold of perception
• Discrimination operational definition


  Smallest intensity difference (delta I) between 2 stimuli which can be detected 50% of the time
• Weber’s law marketing


  Negative changes are not desirable to the public,

  Product improvements are very APPARENT to consumers without being that good
• Absolute threshold does not consider

  Response bias
• Response bias 


  tendency of participants in a survey or experiment to respond in a certain way regardless of their true feelings or thoughts
• Response bias measures


  -conservative (tendency to NO if in doubt)

  -neural

  -liberal (tendency to YES if in doubt)

  -expectations high: liberal

  -expectations low: conservative
• How to deal with response bias

  Signal detection theory/method
• Signal detection theory 


  Able to distinguish sensitivity from response bias; introduces ‘noise trials’ (No signal) in addition to ‘signal trials’ (weak singnal).

  uses means of proportions of hits and false alarms
• How the nervous system processes light

  Electromagnetic spectrum and visible light;

  physical stimulation- wavelength/intensity

  psychological sensation- colour/brightness
• Sensory adaptation 


  Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while(strong smell of cookies)
• Habituation


  The tendency of the brain to stop attending to constant, unchanged situation
• The brain is interested in

  Contrast - rel difference in the amount coming from two lications - contour
• Contrast signal =


  Infromation
• Contrast signal process 


  Light- photoreceptors- bipolar cells- ganglion cells- optic nerve
• Bipolar sells


  Specialized neurons found in the retina of the eye that transmit signals from photoreceptor cells (rods and cones) to ganglion cells.
• Ganglion cells


  Specialized neuron found in the retina of the eye that receives inputs from bipolar cells, which in turn receive input from photoreceptor cells. The ganglion cells then send the processed visual information out of the retina through their axons, which converge at the optic disc to form the optic nerve.
• Perceptual reconstruction process

  Perception produces an INTERPRETATION of the world, not a perfect representation of it
• Percept


  The meaningful product of perception