Measuring unconscious cognition: Beyond the zero-awareness criterion

Abstract

Visual masking can be employed to manipulate observers' awareness of critical stimuli in studies of masked priming. This paper discusses two different lines of attack for establishing unconscious cognition in such experiments. Firstly, simple dissociations between direct measures (D) of visual awareness and indirect measures (I) of processing per se occur when I has some nonzero value while D is at chance level; the traditional requirement of zero awareness is necessary for this criterion only. In contrast, double dissociations occur when some experimental manipulation has opposite effects on I and D, for instance, increasing priming effects despite decreasing prime identification performance (Schmidt & Vorberg, 2006). Double dissociations require much weaker measurement assumptions than other criteria. An attractive alternative to this dissociation approach would be to use tasks that are known to violate necessary conditions of visual awareness altogether. In particular, it is argued here that priming effects in speeded pointing movements (Schmidt, Niehaus, & Nagel, 2006) occur in the absence of the recurrent processing that is often assumed to be a necessary condition for awareness (for instance, DiLollo, Enns, & Rensink, 2000; Lamme & Roelfsema, 2000). Feedforward tasks such as this might thus be used to measure the time-course of unconscious processing directly, before intracortical feedback and awareness come into play.

Keywords: dissociations; feedforward sweep; masking; priming; response; visual awareness.

Figure 1.

Data patterns and assumptions necessary to interpret a simple dissociation as evidence for nonzero unconscious information. An arrow from information source a to measure B indicates that B is some function of a. S-shaped inset symbols denote that weak monotonicity is assumed for that function. Abbreviations as explained in main text. a) Data pattern required for a simple dissociation. Direct and indirect measures are plotted in an opposition space in effect size units. Evidence for a simple dissociation is given by data points lying on the stippled vertical line such that I > 0 while D = 0. b) A simple dissociation gives evidence for nonzero unconscious information if it can be assumed that D is an exhaustive function of c and that I is a weakly monotonic function of u. c) Alternatively, a simple dissociation gives evidence for nonzero unconscious information if I is an exclusive measure of u. Adapted from Schmidt and Vorberg (2006).

Figure 2.

Data patterns and assumptions necessary to interpret a double dissociation as evidence for nonzero unconscious information. a) Data pattern required for a double dissociation. Evidence for a double dissociation is given by any pair of data points that can be connected by a straight line with negative slope anywhere in D-I space. b) A double dissociation gives evidence for nonzero unconscious information if it can be assumed that I and D are weakly monotonic functions of c. Further assumptions need not be made, leaving c and u to interact freely on both measures. Adapted from Schmidt and Vorberg (2006).

Figure 3.

a) Experimental tasks and procedures employed by Schmidt (2002) and Schmidt et al. (2006). b) Stimulus conditions were varied by crossing two levels of color contrast (for primes and masks together) with two types of masks (“strong” metacontrast masks or “weak” pseudomasks). c) Stimulus conditions had large effects on prime identification performance. The 17-ms SOA condition refers to a second experiment not reported here. Adapted from Schmidt et al. (2006).

Figure 4.

Priming effects in pointing movements in the mask identification task of Schmidt et al. (2006). a) Low-contrast color conditions. b) High-contrast color conditions. Note that the time axis is locked to prime onset while the possible times of mask onsets are indicated by the stippled vertical lines. Priming effects were calculated by subtracting finger positions in consistent and inconsistent trials. Vertical bars correspond to within-subject standard errors at several points in time, pooled across subjects. Note that in both color contrast conditions, the initial time-course of priming is identical for all SOAs and both mask types, strongly suggesting that early priming effects exclusively depend on properties of the prime but are independent of all mask characteristics. Adapted from Schmidt et al. (2006).