Chapter 1: Sensation and Perception

Question 1

What’s the major difference between sensation and perception?

Answer 1

• Sensation - stimulation of the sensory organs (ex. touching a fuzzy surface)
• Perception - Organizing sensory information into representations of the physical stimulus (ex. registering the fuzzy surface as a blanket).

Question 2

What’s one thing to note about sensation and perception?

Answer 2

• Perception comes after sensation
• This makes sense since perception gives meaning to all the sensory signals we receive. It also occurs automatically

Question 3

What’s an important step that occurs between sensation and perception?

Answer 3

• Transduction. Turns sensory stimuli into neural signals that can be sent to and interpreted in the brain.
• Turns physical dimensions into perceptual dimensions (ex. wavelength into colour)

Question 4

What are the two types of environmental stimuli and their respective definitions?

Answer 4

• Distal - The thing in the world seen at a distance (ex. a tree)
• Proximal - The physical phenomenon that impinges on sensory receptor cells (the light waves reflecting off the tree and into your eyes)

Question 5

What is the Principle of Neural Representation?

Answer 5

• All that we perceive is not based on direct contact with stimuli but on representations (neural codes) in the receptors and brain
• Same occurs when visualization in the mind is happening

Question 6

What happens after a signal from a stimulus is transduced to the brain?

Answer 6

• They go to their respective primary receiving area in the brain.
• Each sense has its own general area, differing in size

Question 7

What’s the difference between a primary processing centre and association areas?

Answer 7

• Primary processing centres is where the signal first travels to when it arrives in the brain
• Association areas are where the brain attempts to coordinate and organize the different senses in order to perceive the surroundings.

Question 8

Why is neural processing so important?

Answer 8

• Required to form an integrated conscious experience, store it in memory etc.
  *Some info may be sensed, but not attended to.

Question 9

What are the two types of neural processing?

Answer 9

• Bottom-up processing - processing based on the stimuli reaching the receptors (ex. getting a paper cut)
• Top-down processing - an observers knowledge, expectations, and goals, all of which can affect perception (ex. reading)

Question 10

Who is the scientist responsible for developing the field of psychophysics?

Answer 10

• Gustav Fechner (early to late 19th century)

Question 11

What were the three ways that Fechner devised to empirically evaluate the mind?

Answer 11

1) Absolute threshold
2) Difference threshold
3) Magnitude estimation (correspondence between physical and perceptual magnitudes)

Question 12

What was the initial definition of absolute threshold?

Answer 12

• The minimum stimulus intensity that can just be detected by the brain
• Meant to represent the boundary between sensing and not.

Question 13

What were the three classical methods used for determining the absolute threshold for an individual?

Answer 13

• Method of limits
• Method of adjustment
• Method of constant stimuli

Question 14

What’s the method of limits?

Answer 14

• A reasonably quick and fairly accurate way of classically measuring the absolute threshold.
• Experimenter presents a stimulus of a given intensity and continuously asks participants if they can detect the stimulus. They will increase or decrease the stimulus depending on their response.
• Boundary value is taken and process is repeated but this time started in the other direction

Question 15

What’s the method of adjustment?

Answer 15

• A quick and dirty, classical estimate of the absolute threshold
• Start at a given stimulus intensity and the participant is able to increase or decrease the intensity of the stimulus until they identify the threshold level.
• Not as precise as the participant may overshoot the boundary since they may not be that sensitive
• The process is repeated, and the average is taken

Question 16

What’s the method of constant stimuli?

Answer 16

• The most time-consuming but most accurate classical method in determining the absolute threshold
• 5-9 selected stimuli of ‘constant’ intensities are repeatedly presented in a random order. These results are then graphed as a probability of detection

Question 17

What new definition of the absolute threshold was derived from the method of constant stimuli?

Answer 17

• Absolute threshold - lowest intensity necessary for a stimulus to be detected 50% of the time.

Question 18

What does it mean to have a lower threshold?

Answer 18

• Means you are more sensitive to lower levels of stimulus

Question 19

How does adaptive testing work?

Answer 19

• Builds off the method of limits but is much more efficient
• each time a response changes, the direction of the stimulus also changes (also called the staircase method)
• End up hovering/oscillating over a specific value, that being your threshold
• Everything depends upon the participant’s response

Question 20

What’s the difference threshold?

Answer 20

• Also called the just-noticeable difference (JND)
• The smallest difference between two stimuli that people can detect (50% of the time)
• The minimum difference between 2 stimuli before you can tell they are different

Question 21

How is the difference threshold/JND measured/determined?

Answer 21

• Using Weber’s law which states that the size of the JND is proportional to the magnitude of the first stimulus
• Each type of stimulus has its own constant fraction that’s used
• As stimulus get more intense, the difference must also increase for us to be able to perceive it (or constant difference get less and less noticeable)

Question 22

What does psychophysical scaling involve?

Answer 22

• An attempt to discern whether perception matches/corresponds to the changes in sensation/environmental changes.
• Varies for each sense

Question 23

What’s response compression vs. response expansion?

Answer 23

• Terms used in psychophysical scaling.
• Response compression - don’t perceive gradual increases in stimulus as to what the environment reflects (this is the case with brightness)
• Response expansion - Perceive the change in sensation much greater than it actually was (this is the case when experiencing pain)

Question 24

What does Steven’s Power law describe?

Answer 24

• The relationship between physical and perceived intensity follows the same equation across all values of a stimulus type
• P = KS^n (the constant is not super relevant)

Question 25

What’s the purpose of the Signal Detection Theory?

Answer 25

• Want to differentiate people’s perception to a change in stimulus as valid or not (are they actually super-sensitive or just less conservative?)
• A decision criterion is set to ensure the person is actually detecting the stimulus or not
• Sometimes the stimulus will change, sometimes it won’t. These are often referred to as catch trials.

Question 26

What are other influences on threshold?

Answer 26

• Personality
• Level of fatigue/attention (too tired can cause you to miss the stimulus)
  -Rewards/cost
• Noise that interferes with the individual’s ability to catch the stimulus

Question 27

True or false: There is a fixed level of sensitivity.

Answer 27

• FALSE
• Perception depends on sensation and cognitive processes (as indicated by the signal detection theory)
• There’s no fixed level of sensitivity