Cognitive Psychology

Q. Signal detection theory is an outgrowth of classical psychophysics. Explain how. Also discuss the use of ROC payoff matrix for discerning the mechanisms of  higher cognitive processes like decisions making. ( 5+5) Marks.

4 thoughts on “Cognitive Psychology”

  1. Classical psychophysics was mainly focused on finding a relationship between the physical energy availed by stimulus to our senses and the sensation which we receive. It ignored the fact that organismic factors like expectation and motivation indeed play a role. The key pioneers were Wegner and Fechner.

    The signal detection theory can be said to be an extension of Classical Psychophysics in detecting the signal. It’s an outcome of theorists who believed that organismic factors does play a role along with psychophysics.

    It further explains dilemma that there can be different outcomes based on different criteria set for detection.

    For example: we can have a YES BIAS – take a case where missing a signal is penalty and then FALSE ALARM will increase however MISS will be less, and NO BIAS – where detecting a wrong signal is costly and then MISS may increase while FALSE ALARM will be low.

    And here comes the role of ROC payoff matrix.
    ROC matrix helps us to set an optimal criteria.
    Let’s see a graph with FALSE ALARMS as X-Axis and HIT as Y-Axis.
    Now we can plot the cases wit different criteria and the outcome of signal detection.
    Thus we can easily select the graph where the HIT is increasing more sharply. Like- if HIT is the Y-Axis then the graph which is above and more sharp than others is more optimal to select.
    This way this new theory helps us to get minimum error score and maximum true score.

  2. Psychophysics is the study of the relationship between physical stimuli and the sensations they evoke in human being. Classical psychophysics deals with measurement of such sensation. Signal detection theory is an outgrowth of classical psychophysics as it involves measurement of both sensation and criterion human beings use to perceive sensitivity.
    Signal detection theory can be used in demonstrating how human beings make decisions or perceive stimulus during uncertainty. Suppose a radiologist has to examine a CT scan and detect if there is any tumour. The task has four possible responses:
    • There is a tumour and radiologist detects and responds” yes”(HIT)
    • There is no tumour, but she says” yes”(FALSE ALARM)
    • There is a tumour, but she says “no”(MISS)
    • There is no tumour and therefore she says “no”(CORRECT REJECTION)
    Signal detection theory is used and a graph can be plotted on “HIT” and “FALSE ALARM” probabilities. The curve represents the ROC(Receiver Operating Characteristics). In the above example, radiologist considers two factors in decision making:
    1. Presence of stimulus signal: She observes the scan, checks for the presence of tumour base on size/color and then likelihood of “HIT” and “FALSE ALARM” occurs
    2. Judgement: Decision to decide whether there is a stimulus(tumour) depends upon individual’s motivation, bias which is the result of expectation. If she is liberal and has bias towars “YES”, She will say so even though there is no enough evidence to say so. On the contrary, if she is conservative and needs enough evidence to say yes , but could not have such evidence, she says “NO”
    Calculation of d’(measure of sensitivity) and C( response bias) is also a part of analysis of ROC matrix. Signal detection theory thus provides a means of analysing choices and evaluating how effectively they are made.

  3. The psychophysics founded by Gustav Fechner, measured the threshold of stimuli, relative to each other to know the responses of individual towards them. Earlier absolute threshold was used, then difference threshold. These had practical application, like how what smell should LPG leak should have in order to be detected.

    The was further extended to SDT, which is a further enhancement, as it states that our abilities to detect signal depends not just on the intensity but also on many internal factors. Like on a battle front, army men might be more attentive owing to physical arousal than when they are on normal patrolling.

    Receiver operating characteristic payoff matrix gives the basis for understanding non sensory factors underlying response biases in higher cognitive process. Like when the reward for the Hit are highs and cost for the false alarm is low, the observer will be biased to detect the stimuli, and in a way this will increase number of false alarm cases. Likewise when the reward for correct rejection is high and cost for miss are low the observer will be biased not to detect the stimuli.

    Therefore in a setting like vigilance, airport radars surveillance such pay offs becomes important and the ROC payoff matrix and SDT plays important role.

  4. Classical psychophysics only focused upon the physical relationship between stimulus (its energy) and sensation, whereas Signal Detection Theory takes into account the cognitive factors such as motivation and perceptual readiness of the observer. In signal detection theory, organismic variance is taken into account, which was absent in theories given by Weber and Fechner. Ergo, we can say that SDT is an outgrowth of classical psychophysics as it improves upon the research that had already been done and proven in classical psychophysics.

    ROC payoff matrix is a bias/motivation analysis of the observer. It helps in better decision-making. There can be four outcomes based on either a “yes” bias, or a “no” bias of the observer. If the stakes of missing a signal are high, the observer will be having a “yes” bias and the error he’s prone to commit will lead to a “false alarm”. If the stakes are not too high, the observer will be having a “no” bias, which will give an error result of a “miss”. There errors are not in isolation, rather in combination with correct responses of a “hit” and “correct rejection”, respectively, in the previous two cases.

    Plotting the responses helps in identifying the correctness in detecting the signals and the appropriateness of decision taken. Ergo, we can say that Signal Detection Theory is a useful tool for discerning the mechanisms of higher cognitive processes like decision-making.

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