Causal events enter awareness faster than non-causal events

Abstract

Philosophers have long argued that causality cannot be directly observed but requires a conscious inference (Hume, 1967). Albert Michotte however developed numerous visual phenomena in which people seemed to perceive causality akin to primary visual properties like colour or motion (Michotte, 1946). Michotte claimed that the perception of causality did not require a conscious, deliberate inference but, working over 70 years ago, he did not have access to the experimental methods to test this claim. Here we employ Continuous Flash Suppression (CFS)-an interocular suppression technique to render stimuli invisible (Tsuchiya & Koch, 2005)-to test whether causal events enter awareness faster than non-causal events. We presented observers with 'causal' and 'non-causal' events, and found consistent evidence that participants become aware of causal events more rapidly than non-causal events. Our results suggest that, whilst causality must be inferred from sensory evidence, this inference might be computed at low levels of perceptual processing, and does not depend on a deliberative conscious evaluation of the stimulus. This work therefore supports Michotte's contention that, like colour or motion, causality is an immediate property of our perception of the world.

Keywords: Binocular rivalry; Consciousness; Continuous flash suppression; Perception of causality; Visual awareness.

Figure 1

(A) Events used in both experiments. In the launch event (Experiments 1 and 2), a disc starts moving toward a stationary disc, stops right in front of it, and the stationary disc then starts moving. In the pass event (Experiments 1 and 2), a disc starts moving toward a stationary disc, stops when it fully overlaps with the stationary disc, and the stationary disc then starts moving. In the pseudo-launch event (Experiment 2), a disc starts moving toward a stationary disc, and stops after passing by the side of the stationary disc, after which the stationary disc starts moving. (B) Trial sequence used in the experiments. After a fixation period (1 s), the moving CFS mask was presented to the dominant eye and the (non-) causal event to the other eye. The disc events repeated and gradually increased in contrast until observers detected any part of the discs. In the second frame, the first disc is not drawn as a full disc because it appears from behind the virtual occluder.

Figure 2. Results of Experiment 1.

(A) Bar plot depicting mean suppression times for both event types. Errors bars are 95% within-subject confidence intervals. (B) Plot depicting the effect of event type for each observer separately (gray) and across all observers (black, difference between the bars in the left figure). Dots depict the mean difference between suppression times from pass and launch events, where positive values indicate that launch events entered awareness faster compared to pass events. Lines indicate 95% bootstrapped confidence intervals (based on 10,000 bootstrap samples). Almost all dots lie to the right of a zero difference, indicating that launch events enter awareness faster than pass events for nearly every observer.

Figure 3. Results of Experiment 2.

(A) Bar plot depicting mean suppression times for all three event types. Errors bars are 95% within-subject confidence intervals. (B) Plot depicting the effect of event type for each observer separately (gray) and across all observers (black, difference between the bars in the left figure). Dots depict the mean difference between suppression times from pass and launch events, where positive values indicate that launch events entered awareness faster compared to pass events. Squares depict the same information, but now for launch vs. pseudolaunch events. Lines indicate 95% bootstrapped confidence intervals (based on 10,000 bootstrap samples). Most of the data points lie to the right of a zero difference, indicating that launch events enter awareness faster than pass or pseudolaunch events.