5.2 Detection requires a certain amount of the stimulus

Question 1

Graph showing absolute threshold

Answer 1

Question 1

Explain sensory thresholds

Answer 1

• Your sensory organs constantly acquire information from your environment, much of which you don’t notice
• It has to surpass some level before you can detect it
• The absolute threshold is the minimum intensity of stimulation that must occur before you experience a sensation (the stimulus intensity you would detect 50% of the time)
• E.g. how loudly must someone in the next room whisper for you to hear it. In this case, the absolute threshold for auditory stimuli would be the quietest whisper you could hear half the time

Question 2

Difference threshold (just noticeable difference)

Answer 2

• The smallest difference between two stimuli that you can notice
• E.g. the minimum change in the volume of a TV required for you to detect a difference
• The difference threshold increases as the stimulus becomes more intense. Pick up a 1-ounce letter and a 2-ounce letter, and you will easily detect the difference.
• But pick up a 5-pound package and a package that weighs 1 ounce more, and the difference will be harder, maybe impossible, to tell.
• The principle at work here is called Weber’s law.

Question 3

Weber’s law

Answer 3

• This law states that the just noticeable difference between two stimuli is based on a proportion of the original stimulus, rather than on a fixed amount of difference
• The more intense the stimulus, the bigger the change needed for you to notice

Question 4

Signal detection theory

Answer 4

• People are bombarded by competing stimuli, including the ‘noise’ produced by both internal stimuli (moods, emotions, memory, physical states such as arousal or nausea), and other external stimuli e.g. wind). The competing internal and external sources affect judgment and attention.
• Signal detection theory (SDT) states that detecting a stimulus is not an objective process, but rather a subjective decision with two components: (1) sensitivity to the stimulus in the presence of noise and (2) the criteria used to make the judgment from ambiguous information

Question 5

Payoff matrices for signal detection theory

Answer 5

Question 5

Response bias

Answer 5

• A participant’s tendency to report or not report detecting the signal in an ambiguous trial
• The participant might be strongly biased against responding and need a great deal of evidence that the signal is present
• Under other conditions, the same participant might need only a small amount of evidence

Question 6

Sensory adaptation

Answer 6

• A decrease in sensitivity to a constant level of stimulation

Question 7

Hit, miss, and false alarm

Answer 7

Hit: the signal is presented and the participant detects it

Miss: the participant fails to detect the signal

False alarm: the participant reports that there was a signal that was not presented