Measuring Perception

• Why is perception important to study?

  It takes up 50% of the cortex - a lot of neural real estate is devoted to perception.
• What does psychophysics measure?

  Perceptual responses to varying properties of stimuli.
• What is manipulation in psychophysics?

  Making a stimuli harder or easier to see, contrasting effects and adaptation involving long-term exposure to the stimuli.
• What is typically measured in psychophysics?

  The percentage of stimuli guessed correctly, this is used to estimate an individual's threshold.
• Regarding measurement in psychophysics, what is an individual's threshold?

  The lowest quantity of stimulus that a person can perceive.
• How is stimuli presented in psychophysics?

  Very subtle or may not be visible and are presented for very short periods of time.
• What is stimuli in psychophysics?

  It is simple and stylistic.
• Regarding stimuli in psychophysics, what is the perceptual community interested in?

  Stimulus composition and how the stimulus in constructed and what it contains.
• What are the primary and secondary measures in psychophysics?

  Accuracy is the primary measure and reaction time is secondary or ignored altogether.
• What is measured in vision in psychophysics`?

  Intensity of light, contrast, colour, orientation, size, depth, motion, textures, or objects.
• What is measured in sound in psychophysics?

  Loudness, pitch, or direction.
• What is measured in touch in psychophysics?

  Intensity, positioning, and texture.
• What is measured in taste in psychophysics?

  Intensity, flavour, and texture.
• What is measured in smell in psychophysics?

  Intensity and odour.
• What is contrast sensitivity?

  Participants are shown thicker and thinner lines with the same contrast. The thickest and thinnest lines are the hardest to identify - participants have to choose which side the lines are on when presented with a blank screen.
• What has contrast sensitivity shown?

  That visual perception varies with the size of striped and with age.
• Regarding noise, what happens when a stimulus in more invisible?

  There is a lot of noise and participants are more likely to say they cannot see it.
• What is a change in criterion for saying yes?

  Participants say yes to seeing a stimuli because they want to - this may be due to comfort, or trying to appear not blind or deaf.
• What is a change in bias?

  When the tendency to say yes changes between groups, older adults are more likely to say no because they are uncertain about seeing weak and brief stimuli.
• What are the problems with bias in perception experiments?

  There are problems with drawing conclusions and calculating thresholds. Participants being more willing to say yes will shift axis.
• What are spatial intervals?

  Stimuli is presented on one side and a blank on the other side of a focus cross. Participants have to indicate which side the stimuli was on.
• What are temporal intervals?

  A stimulus is shown before a blank or after a blank, participants have to decide which of the intervals the stimuli appeared on.
• What is a forced choice task?

  Participants are only allowed to select one of two answers (yes/no, left/right, first/second) there is no 'I don't know' option.
• Where is the threshold normally placed in the forced choice psychometric function?

  Between the 50 and 100 mark, as participants tend to plateau at 50/50.
• What is a single interval symmetric choice task?

  Participants are presented with a vertical or horizontal stimulus and must say whether it is vertical or horizontal - this avoids yes/no bias.
• Why is the two interval forced choice task used with vertical or horizontal stimuli?

  Fine-grained variations can be made for orientation and can look to see the smallest amount of orientation change that can be detected.
• What is system characterisation?

  Manipulation of the stimulus to change the threshold the person has in response to that stimulus - experimenters manipulate features of a stimulus that would otherwise be similar to the original.
• What is simultaneous masking?

  Increments are added to a pedestal to emphasise one stimulus.
• What is simultaneous facilitation?

  Weak pedestals make increments easier to see.
• What is sequential masking?

  A strong stimulus appears before a weaker stimulus - this makes the weaker stimulus harder to see.
• What is sequential priming?

  When the stimulus is weak and the stronger stimulus follows it - weak primes make subsequent stimuli easier to see.
• Describe a facilitator/prime.

  Tend to be weak and similar to the stimulus (but not identical). They are detected by the same cells that detect the stimulus.
• Describe a mask.

  Masks are strong and can be different or the same as the stimulus (the more different they are the less effective). They are detected with the same large pool or cells that detect the stimulus.
• What is measuring appearance by adjustment?

  Participants are shown the stimulus on one monitor and must adjust a prompt on the other monitor to match the stimulus.
• Regarding measurement, what is a single interval symmetric choice task?

  Participants are presented with a stimulus and asked to identify whether it is tilting left or right.
• In the single interval symmetric choice task, what is the point of subjective equality?

  The point where participants cannot tell if the stimulus is tilted left or right.
• What is simultaneous presentation?

  Two discs are presented, one straight lined within another tilted line disc.
• What are the conditions for changing the central disc?

  Stimuli must be similar to the one you are trying to manipulate and it must be within 15 degrees of orientation.
• What is sequential presentation?

  The stimulus is presented for a long period and then taken away, a following stimulus is presented. This can affect the perception of the second stimulus.
• What is the method of constant stimuli?

  A fixed set of stimuli is chosen in advance, they are then presented at random and participants are asked to indicate which interval they are in.