3.1 How the Physical World Relates to the Psychological World

How could Stevens's Power Law be understood as an adaptation enhancing our survival?

*1. serves a protective function* • i.e. protecting our eyes and ears from dramatic increases in sensory intensities *2. alert us to possible dangers* • i.e. increasing the perceived intensities of dangerous stimuli like electric shock

Weber's Law

*Difference Question* required difference in sensory judgement is a proportion (constant fraction) of the original stimulus intensity • Brightness = 8% • Loudness = 5% • Weight = 2%

Stevens's Power Law

*Scaling Question* to equal the *perceived intensity*, the actual physical intensity has to be raised to some constant power, and this constant is different for each type of sensory judgment

Difference Question (with example)

*concerned with our ability to detect very small differences between stimuli* i.e. what is the *smallest difference* in brightness/ loudness between two lights/ sounds that we can see/hear?

*4 Possible Outcomes in a Signal Detection Study*

*hit* - *correctly* detecting a signal when one was presented *correct rejection* - *correctly* saying a signal was not presented when it was not *false alarm* - saying a signal was presented when it was not *miss* - failing to detect a signal when one was presented

Signal Detection Theory

*our ability to detect a faint sensory signal (stimulus) is a decision-making process that depends upon a person's:* • physiological sensitivity to the signal • decision-making criterion (based on nonsensory factors such as personality traits, expectations, alertness, and motivation)

What do a smaller and larger constant in Weber's Law indicate?

*smaller constant:* small differences in stimuli change can be easily perceived *larger constant:* indicates a larger proportion of the standard stimulus is necessary for a difference to be perceived

standard stimulus vs. comparison stimulus (with example)

*standard stimulus* - intensity remains the same *comparison stimulus* - intensity changes across trials i.e. standard stimulus for judging differences in lifted weights might be 20 pounds, and the comparison stimuli would be various weights less than or greater than 20 pounds, varying on each trial

In everyday life, what does Weber's law indicate?

1. we notice proportional differences and not absolute differences 2. our ability to perceive a difference is relative to the constant background intensity • i.e. in a dimly lit room, a little bit of light will be noticed; but in a brightly lit room, it will take a much greater increase in light to be noticed

subliminal perception

perception of or reaction to a stimulus that occurs without awareness or consciousness

The *detection* and *difference* questions examine limits on our _____

sensory processing

subliminal stimuli

stimuli detected up to 49 percent of the time

T or F - Our perception of even a faint signal is a subjective process impacted by non sensory factors?

True

T or F - humans are pretty good detectors of weak stimuli?

True

limits on sensory adaptation

We don't adapt to: *1. extremely intense/ painful stimuli* • severe toothache/ extremely loud noises *2. unchanging visual stimuli* • our eyes are constantly moving so their visual images continue to change

How do researchers measure signal detection?

a signal of constant faint intensity is present or not present, and the observer decides with a "yes" or "no" wether a signal is present

From an evolutionary viewpoint, why does sensory adaptation makes sense?

changes are more likely to signal danger in our environment than things that don't change

Scaling Question (with example)

concerned with *how we perceive the intensities* of clearly detectable stimuli i.e. if we double the physical intensity of a light/sound, do we see it as twice as bright/loud? (answer is no)

Detection Question (with example)

concerned with the limits on our ability to detect very faint signals i.e. how intense does a light/ sound have to be for us to see/hear it?

Because the detection task is a _____ involving _____, sensory researchers prefer to use _____ to describe our detection abilities

decision-making process, a response criterion, signal detection theory

psychophysical research

focuses on the relationship between the physical world and the psychological world

What do psychophysical researchers attempt to answer?

how we process the intensities of physical energy forms such as light waves and sound waves

Explain the constant power of Stevens's Power Law

if the constant power is 1, the perceived magnitude equals the physical magnitude - this is seldom the case, except when we judge line lengths (if a line is doubled we perceive its length as doubled) • brightness = 8-9x increase in light results in perception of 2x brighter • pain = 2x increase in electric shock results in perception of 10x more intense

According to signal detection theory, what would happen to a person's false alarm and miss rates if the person switched from a very lax to a very strict decision criterion?

lax to strict decision criterion = false alarm rate goes down / miss rate would goes up (changing from saying "yes" most of the time to saying "no" most of the time)

How is the detection question measured?

measuring the *absolute threshold* - the minimum stimulus intensity that can be detected 50 percent of the time (equal probability of being detected or not detected)

How is the difference question measured?

measuring the *difference threshold* - minimum difference between two sensory stimuli detected 50 percent of the time

sensory adaptation

our sensitivity to unchanging and repetitious stimuli disappears over time

Weber's law holds for most types of sensory judgments except for what?

very low-intensity or high-intensity stimuli

Why were absolute and difference thresholds given statistical definitions?

when psychophysical researchers attempted to measure the absolute and difference thresholds, experimental data did not permit an absolute definition there was no none-to-all point of change in the results that were observed

What are the three psychophysical questions?

• detection • difference • scaling

What can we conclude for almost all types of sensory judgment?

• the scales of measurement are *not equivalent*, however they are *lawfully related*