Number processing outside awareness? Systematically testing sensitivities of direct and indirect measures of consciousness

Abstract

In priming research, it is often argued that humans can discriminate stimuli outside consciousness. For example, the semantic meaning of numbers can be processed even when the numbers are so strongly masked that participants are not aware of them. These claims are typically based on a certain pattern of results: Direct measures indicate no conscious awareness of the masked stimuli, while indirect measures show clear priming effects of the same stimuli on reaction times or neurophysiological measures. From this pattern, preserved (unconscious) processing in the indirect task is concluded. However, this widely used standard reasoning is problematic and leads to spurious claims of unconscious processing. Such problems can be avoided by comparing sensitivities of direct and indirect measures. Many studies are affected by these problems, such that a reassessment of the literature is needed. Here, we investigated whether numbers can be processed unconsciously. In three experiments, we replicated and extended well-established effects of number priming over a wide range of stimulus visibilities. We then compared the standard reasoning to a sensitivity analysis, where direct and indirect effects are compared using the same metric. Results show that the sensitivities of indirect measures did not exceed those of direct measures, thereby indicating no evidence for preserved unconscious processing when awareness of the stimuli is low. Instead, it seems that at low visibility there is residual processing that affects direct and indirect measures to a similar degree. This suggests that similar processing modes cause those effects in direct and indirect measures.

No effect of attentional modulation by spatial cueing in a masked numerical priming paradigm using continuous flash suppression (CFS)

“…To put it simply, our data provide no support for the “CFS-attenuation-by-inattention” hypothesis and suggest that there might be “not much to see” under CFS, or even no number processing outside awareness per se ( Zerweck et al, 2021 ). It is conceivable that the large heterogeneity between published CFS findings is due to other factors and choices, e.g.…”

The necessity of equivalent comparisons for interpreting masked priming effects: Implications for studies of unconscious perceptual processing.

“…This result supports Reingold and Merikle, who advocated for the direct versus indirect sensitivity approach (Merikle & Reingold, 1991; Reingold & Merikle, 1988; see also Peters & Lau, 2015; Zerweck et al, 2021). Reingold and Merikle (1988) emphasized the importance of having equal conditions for making the direct versus indirect comparison (p. 566):A critical aspect of the proposed assumption concerning the relative sensitivity of direct and indirect measures to conscious perceptual experience is the assertion that the sensitivity of both indexes should be measured under comparable experimental conditions.…”

“…Another difference is that the preceding experiments involved only target judgments. If the indirect priming effects from the short and the medium duration prime stimuli are valid, this outcome would be consistent with numerous past (Bernstein et al, 1989;Dark, 1988;Dark & Benson, 1991;Purcell et al, 1983) and recent (Balsdon & Clifford, 2018;Benthien & Hesselmann, 2021;Døngart & Kyllingsbaek, 2019;Peters & Lau, 2015;Rajananda et al, 2020;Sand, 2016;Zerweck et al, 2021) studies that report negative findings. However, the Bayesian analyses suggest that the indirect findings are inconclusive for the short and medium duration conditions.…”

“…This result supports Reingold and Merikle, who advocated for the direct versus indirect sensitivity approach (Merikle & Reingold, 1991;Reingold & Merikle, 1988; see also Peters & Lau, 2015;Zerweck et al, 2021). Reingold and Merikle (1988) emphasized the importance of having equal conditions for making the direct versus indirect comparison (p. 566):…”

“…Recent comparisons of direct versus indirect effects suggest that d ′ values for both effects are about equal in masked priming studies (Meyen et al, 2022; Zerweck et al, 2021). The present experimental outcomes are similar, with the short duration condition showing approximately equal d ′ sensitivities of about zero.…”