Signal detection sensitivity and bias

in Table 3.1. The effects of question emphasis on discrimination sensitivity were first analysed via paired-samples t-test conducted for each task separately. For the semantic task, d' was significantly lower for “disagreeable?” compared to “pleasant?”

questions, t(31) = 3.68, p = .001, d = 0.65. There was also a significant effect of question emphasis on sensitivity in the temporal judgement task, such that d' was lower for “second half?” than “first half?” questions, t(20) = 2.21, p = .039, d = 0.49. Question emphasis did not significantly influence d' in the colour and recognition tasks, t(31) = 1.36, p = .183, d = 0.25, and t(27) = 1.06, p = .301, d = 0.20

respectively. The reduced sensitivity for the “disagreeable?” and “second half?” questions is potentially due to the greater difficulty entailed in fluently integrating these questions into ongoing decision-making. For “disagreeable?” questions in the semantic task, this processing difficulty might result from its lower frequency of usage in the English language and associated greater lexical difficulty compared to

123 the alternate “pleasant?” question. For “second half?” questions in the temporal task, the processing difficulty might arise from the dissonance between its featuring the term “second” whilst requiring participants to press the “1” number key to endorse the question (unlike the alternate “first half?” question, for which the numerical descriptor worded in the question is congruent with its method of endorsement via the “1” key). These suggested difficulties in processing the questions themselves would have served to reduce overall sensitivity both by using up pre-decision cognitive resources otherwise directed towards the assessment of evidence

strength5, as well as by increasing the post-decision likelihood of pressing the wrong response buttons.

Admittedly, this interpretation of the question effects on semantic and temporal discrimination sensitivity is speculative, however the discussion of these findings is limited as such given that the primary aim was to interrogate question effects on criterion bias. Nevertheless, the ensuing criterion analyses are complemented by analyses of a measure that takes into account the above variation in sensitivity – c′

(Macmillan & Creelman, 2005). This is simply criterion divided by d′, which serves as a scaling operation that reduces the potential for differences in sensitivity across question emphasis conditions to exert confounding influences on bias.

The analyses of unscaled criterion bias (c) were also conducted via separate paired samples t-tests for each individual task (see Table 3.1. for means; see Figure 3.2.). For the semantic task, c was significantly higher for “pleasant?” compared to

“disagreeable?” questions, t(31) = 6.08, p < .001, d = 1.09. The disconfirmatory or

5

The proposed disruption of evidence-strength processing is comparable to the interference of source monitoring processes following divided attention and response speeding manipulations enacted at recognition test phases, as described in Chapter 1 section 1.3. (Johnson, Kounios & Reeder, 1994; Jacoby, Toth & Yonelinas, 1993).

124 “counter-emphasis” direction of this criterion shift parallels that observed in the

previous chapter, in reflecting the reduced likelihood of endorsing the semantic decision emphasised by the question (i.e. “pleasant?” reduces the likelihood of responding “pleasant”). However, the difference in c across question emphasis conditions in the recognition task was non-significant, t(27) = 0.39, p = .697, d = 0.07. Despite the counter-emphasis direction of this shift in recognition criterion, the failure for the shift to reach significance was contrary to the findings of the previous chapter (in which significant question emphasis effects on recognition criterion were recovered in two separate samples) and an independent study involving a large online sample (Mill & O’Connor, 2014). Further, c shifted in the opposing “pro-

emphasis” direction in the colour and temporal tasks (i.e. reflecting an increased likelihood of endorsing emphasised decisions) albeit to non-significant degrees, t(31) = 1.29, p = .206, d = 0.23, and t(20) = 1.54, p = .138, d = 0.10 respectively (see Figure 3.2.).

Given the previously described effects of question emphasis on d′ sensitivity in the semantic and temporal tasks, the c analyses were complemented by analysis of the sensitivity-scaled bias parameter c′. The pattern of bias results involving c′ was the same as that for unscaled c, with a significant counter-emphasis bias shift observed between question conditions in the semantic task and a non-significant shift in the same direction observed for the recognition task, t(31) = 6.42, p < .001, d = 1.16, and

t(27) = 0.70, p = .489, d = 0.14 respectively (see Table 1 for means). Sensitivity- scaled bias did not differ between question conditions in the colour and temporal tasks, t(31) = 0.77, p = .446, d = 0.13, and t(20) = 0.458, p = .652, d = 0.10

respectively. Collectively, analyses involving both c and sensitivity-scaled c′ reveal that the only reliable effect of question emphasis in shifting response criterion was

125 evidenced in the semantic task. Hence, the overall pattern across the four tasks does not provide compelling evidence in support of cross-domain effects of question emphasis being registered in SDT estimates of bias.

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Table 3.1. Design key and descriptive statistics for cross-task analyses of equal variance signal detection theory (SDT) parameters, including sensitivity (SDT d′), unscaled bias (SDT c) and sensitivity-scaled bias (SDT c′).

Note: M, mean; SD, standard deviation.

Task Semantic Colour Temporal Recognition

Question pleasant? disagreeable? orange? yellow? first half? second half? old? new? Emphasis Decision A Decision B Decision A Decision B Decision A Decision B Decision A Decision B

SDT d′ M 2.29 1.92 2.85 2.99 0.84 0.68 0.92 0.82 SD 0.47 0.49 0.49 0.59 0.38 0.33 0.49 0.38 SDT c M -0.05 -0.41 -0.30 -0.22 0.01 0.11 0.12 0.09 SD 0.35 0.29 0.41 0.40 0.30 0.21 0.38 0.32 SDT c′ M -0.02 -0.22 -0.11 -0.09 0.12 0.19 0.19 0.08 SD 0.16 0.20 0.15 0.16 0.66 0.66 0.82 0.55

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Figure 3.2. Question emphasis effects on equal variance (EV) estimates of criterion bias (c) across the four presented tasks: a. semantic task, b. colour task, c. temporal task and d.

recognition task. In each panel, graphs depict shifts in criterion bias according to the decision emphasised by the question, such that increasing c values reflect a reduced

likelihood of endorsing the “Signal A” decision (i.e. “pleasant”, “orange”, “first half” and “old” decisions respectively; see Figure 3.1. for further detail on this formalization). Error bars represent standard error of the mean.

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3.3.3. Decision accuracy. Question emphasis effects were also examined on the