Working memory can compare two visual items without accessing visual consciousness

Consciousness and Cognition 78 (2020) 102859

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Consciousness and Cognition journal homepage: www.elsevier.com/locate/concog

Working memory can compare two visual items without accessing visual consciousness

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Shun Nakano , Masami Ishihara Department of Human Sciences [Psychology], Tokyo Metropolitan University, 1-1 Minamiosawa, Hachioji, Tokyo 192-0397, Japan

A R T IC LE I N F O

ABS TRA CT

Keywords: Visual working memory Delayed match-to-sample task Unconscious cognitive process

Recent studies argued that unconscious visual information could access the working memory, however, it is still unclear whether the central executive could be activated unconsciously. We investigated, using a delayed match-to-sample task, whether the central executive is an unconscious process. In the experiment of the present study, participants were asked to compare the locations of two given visual targets. Both targets (or one of the two targets, depending on the experimental condition) were masked by a visual masking paradigm. The results showed an above-chance-level performance even in the condition that participants compared two unconscious targets. However, when the trials with the non-visual conscious experience of the target were removed from the analysis, the performance was no longer significantly different from chance level. Our results suggest that the central executive could be activated unconsciously by some level of stimulus signal, that is still below the threshold for a subjective report.

1. Introduction The conscious visual world spreading in front of us is an internal representation that is constructed through the visual input from the retina. We as humans believe that our behavior is executed through the conscious visual experience. However, due to the discovery of the blindsight (Pöppel, Held, & Frost, 1973; Weiskrantz, Warrington, Sanders, & Marshall, 1974), it was revealed that visual consciousness is not required for all goal-directed behaviors. If the visual consciousness has a functional role in human behavior, at which level of the visual information processing, from perception to action, will the visual consciousness be situated? Visual information without a visual conscious experience (unconscious visual information) can be processed at almost all levels of the visual perceptual system (Kouider & Dehaene, 2007; Rees, Kreiman, & Koch, 2002). Recently, the relationship between the working memory and the consciousness has been the focus of interest. The working memory with its limited capacity is part of the human memory system that combines temporary storage and manipulation of information in service of cognition (Baddeley & Hitch, 1974; 2010). Besides the storage of memories, it also has the function of attention control which is separated into the visuo-spatial sketchpad, the phonological loop, and the central executive. In general, it has been proposed that the working memory and the consciousness are connected tightly to each other and that the working memory would be operated by conscious information processing (Baars & Franklin, 2003; Baddeley, 2003). Based on this concept, an early study of unconscious visual perception showed a dissociation between a subjective conscious report concerning visual information and detecting it in a recognition task as well as a forced choice detection task (Kunst-Wilson & Zajonc, 1980). Because the storage of visual information without conscious experience is short-lived (Mattler, 2005), it seems that the conscious

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Corresponding author. E-mail addresses: [email protected] (S. Nakano), [email protected] (M. Ishihara).

https://doi.org/10.1016/j.concog.2019.102859 Received 26 December 2018; Received in revised form 30 November 2019; Accepted 3 December 2019 1053-8100/ © 2019 Elsevier Inc. All rights reserved.

Consciousness and Cognition 78 (2020) 102859

S. Nakano and M. Ishihara

experience of visual stimuli is necessary for executing an experimental task, that needs a voluntary response after a temporal delay in a given trial. However, some recent studies indicated that unconscious processes can support perceptual learning (Chong, Husain, & Rosenthal, 2014; Rosenthal, Andrews, Antoniades, Kennard, & Soto, 2016; Rosenthal, Kennard, & Soto, 2010). These findings suggest that visual information without conscious visual experience could be maintained in the long-term memory and consciousness is not necessary for functionalizing all of the memory processes as the bottleneck. Another study indicated that unconscious visual information that is maintained in the working memory can affect visual perceptual detection (Pan, Lin, Zhao, & Soto, 2014), suggesting that the working memory could be functional without the visual consciousness of memorized visual information. In addition, some recent experimental studies argue that the visual working memory operates through unconscious cognitive processing (Bona, Cattaneo, Vecchi, Soto, & Silvanto, 2013; Dutta, Shah, Silvanto, & Soto, 2014; Soto, Mäntylä, & Silvanto, 2011). These studies focused on the visual working memory in its role as memory storage, but its executive function was not discussed properly. The present paper aims to discuss the relationship between unconscious visual processes and the executive function of the working memory. Furthermore, it tries to provide several lines of evidence that the visual conscious experience does not influence the executive function. The central executive of the working memory is assumed to be an attentional control system that allocates attentional resources to the memory storage. It is also assumed to play an important role in supporting efficient memory retention. The ability of goal formation, planning, carrying out goal-directed plans, and effective performance are executive functions in which the central executive is involved (Baddeley, 2012; Lezak, 1982). In an experimental situation using a forced choice task, for example, goal formation and planning would be executed based on the instruction of the experimental task, carrying out plans and effective performance would be executed by feedbacks during performing the task. In a recent model describing the relationship between the executive function and consciousness, a conscious visual input is necessary for setting the goal as well as planning for the task execution (Ansorge, Kunde, & Kiefer, 2014). In this model, because a huge number of alternatives for the task execution is given based on conscious visual input, the conscious information could create flexible responses. By contrast, the unconscious visual information has nothing to do with planning and creating the goal of the task. An action executed via unconscious visual information is selected from a few alternatives fitting to the pre-existing task-control representations created by conscious inputs. Meanwhile, this model is based on studies about unconscious priming, it is still unclear whether the model could apply to goal-directed behavior in unconscious working memory studies. A previous study, which argues an unconscious visual working memory, has used a delayed match-to-sample task in which participants compared a cue stimulus and a test probe stimulus (Soto et al., 2011). In their task, the participants were asked to detect and maintain the information (i.e., visual feature) of the given stimuli, to compare these two visual items internally and make a selective response. Therefore, the visual working memory is necessary to execute the task. The visuo-spatial sketchpad plays a substantial role of maintaining the visual information whereas the central executive plays a role of comparing the process which requires a use of multiply stored visual information. Conscious awareness to the cue stimulus was distracted by the backward masking paradigm, there were two types of measurements in a trial. The task as an objective measurement was a forced-choice in which the participants selected whether the visual feature of the cue and the test probe was the same or different. The subjective measurement, asked just after completing the objective measurement, was that the participants estimated the subjective visibility of the visual cue. The result of the subjective measures indicated that the visual cue was not perceived consciously, nevertheless, the rate of correct responses in the objective measures was above chance level. Similar results were also observed in other studies (Bergström & Eriksson, 2017; Wildegger, Myers, Humphreys, & Nobre, 2015). These previous findings substantiated the claim of a visual working memory, operating through unconscious cognitive processes. This evidence indicates that unconscious visual information can access the visuo-spatial sketchpad, although it is difficult to explain whether all processing of the working memory is unconscious. It has been shown that conscious visual information access the central executive through the visuo-spatial sketchpad (Baddeley, 2003; 2012). If all components in the working memory can be processed unconsciously, that would mean that unconscious visual information could activate the central executive and execute a working memory task unconsciously. The goal of this study was to clarify the functional characteristics of the connection between visual consciousness and the executive function involved in the central executive of the working memory. In particular, we aimed to verify whether the executive function is driven by unconscious visual stimuli using a delayed match-to-sample task, in such a way that participants were asked to compare two unconscious visual items. The task used in previous studies was that the first visual stimulus (the cue) was masked, but the second (the test probe) was unmasked. Thus, there is a conscious input for making selective responses in the task. There is another interpretation from the viewpoint of the executive function of the findings: the conscious visual information, that is available from the conscious test probe, could access the central executive, drive the executive function, and lead to the selective responses in the task. The executive function depends on the conscious input and this process could be driven by conscious information. Therefore, the central executive in the working memory could be involved in this conscious process. If that is true, that the selective responses are made unconsciously, the unconscious visual items could not activate the executive function enough, thus the delayed match-tosample task is not executed. By contrast, based on the recent executive function model (Ansorge et al., 2014), the goal formation and planning for executing the task could be influenced by the task instruction, in that case unconscious information as well as the conscious visual information could drive the executive function. Previous studies of the unconscious working memory used the task of judging the orientation of a masked Gabor patch (e.g., Soto et al., 2011). The recent study which used other visual features also suggested the independence of the working memory from the visual consciousness (Trübutschek et al., 2017). In the study of Trübutschek et al., a masked visual stimulus and a visible distractor were sequentially presented, and the participants were then required to recall the visuo-spatial location of the masked stimulus under a forced-choice condition. Their results showed that the rate of correct responses was above chance-level, any effects for the distractor were not observed. This suggests that the visuo-spatial information without conscious visual experience could be maintained in the 2

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working memory. In addition to that, another recent study using a similar paradigm indicated that two masked visuo-spatial stimuli could be maintained in juxtaposition and recalled in temporal order (Trübutschek, Marti, & Dehaene, 2019). Although these abovementioned studies used a forced recalling task, the execution of the task could also be explained by the function of the short-term memory without utilizing the working memory function. The function of the working memory is not only to maintain the information but also to control a number of visual items. In the forced recalling task, only the unconscious storing of the visual information can be verified, but it cannot verify that the working memory operates unconscious visual information through the central executive. It is therefore still unclear whether the unconscious visuo-spatial information is used in the comparing process under the delayed matchto-sample task. The present study intends to clarify the relationship between the conscious visual experience and the working memory especially the central executive. The purpose of this study includes the following three points: First, verifying whether the visuo-spatial information could operate the stored information in the working memory without conscious visual experience under the delayed match-to-sample task situation. The aim is to first replicate previous findings. Second, examining whether the central executive could be activated under the condition that participants could not experience consciously the key visual information which determines the selective response in the task. Third, investigating whether the central executive involved in the executive function for the task is independent of the visual conscious experience. In our experiment, the participants were required to compare two unconscious items, and we observed whether selective responses could be made through unconscious visuo-spatial information. If the visuo-spatial information could access the central executive and activate the working memory without conscious visual experience, the rate of correct responses should be above chance level in the condition where the participants compare two subjective invisible items. Alternatively, if the working memory is completely independent of the conscious visual experience, the rate of correct responses in the condition where the participants are comparing two subjective invisible items should not be different from the one, where they are comparing a subjective invisible item and a visible item. 2. Material and methods 2.1. Participants Twenty volunteers participated in the experiment (nine females, mean age = 24.57 years, SD = 3.57). All of them were righthanded and reported normal or corrected-to-normal vision, and signed an informed consent statement. Two participants were excluded from all statistical analyses because they selected the same responses for all masked stimuli condition trials. Thus, eighteen participants (nine females, mean age = 24.05 years, SD = 2.57) were fed into the analyses. The present study was approved by the committee of Tokyo Metropolitan University for the protection of human subjects. 2.2. Stimuli All stimuli were presented on a gray colored background (luminance = 43.00 cd/m2). A gray (low contrast target: diameter = 2.86 degree, luminance = 53.13 cd/m2, contrast = 10.53%) or white (high contrast target: diameter = 2.86 degree, luminance = 215.00 cd/m2, contrast = 66.66%) circular visual stimulus was used as a target in the task. The target was experimentally manipulated to appear in one of four spatial quadrants (5 degrees from the center of a monitor). The masking stimulus was composed of four gray-scale noise pattern circles (diameter = 5.01 degree, mean luminance = 73.29 cd/m2, mean contrast = 25.91%). These positions are four spatial quadrants and the center of each circle was overlapped with the center of the target. All stimuli were shown on a 21-inch CRT monitor (EIZO, refresh rate = 85 Hz) and were programmed and generated with the software Presentation (Neurobehavioral Systems Inc.). 2.3. Procedure Two types of experimental tasks were included in a trial: one was the forced choice delayed match-to-sample task and another was the visibility rating task. The visual conscious experience of the target stimuli was distracted by the sandwich masking paradigm (Forster & Davis, 1984; Kimchi, Devyatko, & Sabary, 2018). Participants were seated in a dark room. Their head was positioned on a head-chin rest set at 40 cm away from the screen during the task. The experiment was divided into four blocks. The experimental design of one trial is schematically illustrated in Fig. 1. Each trial began with the presentation of a fixation point appearing in the center of the screen for 500 ms duration. Then the masking stimulus appeared for 500 ms duration followed by the first target stimulus with 50 ms duration (T1). After the presentation of a 50 ms blank screen, the masking stimulus was presented again with 1000 ms duration. After the blank of 1000 ms, the second target (T2) was presented between the masking stimulus presentations, the time condition of the mask-target-mask combination was the same as the T1 presentation. The experimental design was 2 (T1 contrast: high contrast 66.66% & low contrast 10.53%) × 2 (T2 contrast: high contrast 66.66% & low contrast 10.53%) design. Combinations of those two target stimuli were four patterns (CC condition: the high contrast target was presented twice, CNc condition: the high contrast target was presented first then the low contrast target was presented, NcC condition: the low contrast target was presented first then the high contrast target was presented, and NcNc condition: the low contrast target was presented twice). There was a control condition that blanks were presented instead of these targets. After a 1000 ms delay, a comparing response was promoted by a response cue. The participants were instructed to decide the validity of the spatial positions of T1 and T2 (valid/invalid). They required to make the response as fast as they can during an answer cue presentation (duration = 1000 ms) by 3

Consciousness and Cognition 78 (2020) 102859

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Fig. 1. Timeline of the experimental trial. The target stimulus was presented between mask stimuli (four noise-pattern circles). Target stimuli were presented twice in a trial sequence (T1 and T2). Participants were asked to compare the locations of two given visual targets. After the 1000 ms delay periods, participants had to react about whether two target stimuli were presented at the same location or not (forced choice task). Then, the visibility of the T1 and the T2 were rated continuously by the PAS based four-alternative scale (visibility rating task).

pressing a computer numeric keypad: 1, valid; 2, invalid. The valid position means that T1 and T2 were presented at the same position, whereas the invalid position means that the targets were presented at different positions. Participants were instructed to guess the spatial location of each target presentation and select the alternative even if they had not experienced the target stimulus (forced choice task: FC task). They were then asked to provide a rating of visibility of the T1 using a four-point scale based on the perceptual awareness scale (PAS; Ramsøy & Overgaard, 2004), this was answered by pressing a button on the numeric keypad: 1, did not see anything; 2, did not see the target but felt existence of something; 3, saw the target but it was not clear; 4, saw the target clearly (visibility rating task). Following a 500 ms blank, participants provided visibility of the T2 by the same procedure. Answer cues for each visibility rating about T1 and T2 were presented until response. Finally, a full-screen random noise pattern was presented with 1000 ms duration to cancel visual after-effect. The number of the valid trials and that of the invalid trials were the same (12 out of 24 trials in each target contrast condition) and there were 120 trials per participant across all experimental conditions, therefore the chance level of the FC task was set at 50%. There were four blocks in a measurement, the experimental conditions randomized in each of the blocks. There is a possibility that the responses were affected by the previous task (e.g., the FC task) because the response keys for reacting to two tasks were overlapped. For minimizing the effect of the previous task, the long blanks (1000 ms) were set between each of the tasks. Furthermore, the participants were instructed that it was necessary to respond as fast as they can after the response cue of the FC task, however, that they require to answer accurately to their subjective visual experience in the visibility rating task. In addition to that, there was the time pressure (1000 ms) for the selective response in the FC task, but not in the visibility rating task (the response cue was presented until response). 3. Results The results of mean rates of the visibility rating task were shown in the Table 1. In the visibility rating tasks, d' was computed to confirm the effect of the masking stimuli. Trials that participants rated 1 and 2 were classified as “unseen trials.” Similarly, trials rated 3 and 4 were classified as “seen trials.” Using participants’ subjective responses, d' was computed in each condition: hit rate for the T1 and that for the T2 were defined as the seen trials in the NcNc, NcC, CNc, and CC conditions; false alarm rates for both targets were defined as the seen trials in the control condition without targets. The mean d' of the T1 was 0.15 (SD = 0.32) in the NcNc, 0.24 (SD = 0.31) in the NcC, 3.59 (SD = 0.44) in the CNc, and 3.71 (SD = 0.36) in the CC (Fig. 2A). These were significantly different from zero in the low contrast target [NcNc: t(17) = 2.11, p < .050; NcC: t(17) = 3.30, p < .010] and the high contrast target [CNc: t(17) = 34.77, p < .001; CC: t(17) = 44.07, p < .001]. 4

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Table 1 Mean rates of the visibility rating (SD). Condition

Target (Contrast)

Score 1

Score 2

Score 3

Score 4

NcNc

T1 T2 T1 T2 T1 T2 T1 T2 T1 T2

0.58 0.53 0.46 0.01 0.01 0.39 0.00 0.00 0.69 0.73

0.37 0.42 0.48 0.02 0.02 0.47 0.01 0.00 0.28 0.25

0.05 0.05 0.04 0.15 0.16 0.11 0.12 0.11 0.02 0.01

0.00 0.01 0.03 0.81 0.81 0.02 0.86 0.88 0.01 0.00

NcC CNc CC Control

(Low) (Low) (Low) (High) (High) (Low) (High) (High) (no-target) (no-target)

(0.31) (0.27) (0.29) (0.02) (0.02) (0.28) (0.01) (0.01) (0.28) (0.24)

(0.27) (0.23) (0.26) (0.04) (0.03) (0.23) (0.02) (0.01) (0.26) (0.24)

(0.06) (0.1) (0.06) (0.27) (0.28) (0.14) (0.27) (0.21) (0.03) (0.03)

(0.01) (0.02) (0.04) (0.28) (0.29) (0.03) (0.27) (0.21) (0.02) (0.00)

Fig. 2. The mean d’ of T1 (A) and T2 (B) in the visibility rating task. Error bars represented standard error of mean (SEM). A) In the visibility rating about the T1, the low-contrast target stimulus was rated in the NcNc and the NcC condition. On the contrary, the high-contrast target stimulus was rated in the CNc and CC condition. B) In the visibility rating about the T2, the low-contrast target stimulus was rated in the NcC and the CC condition. The high-contrast target stimulus was rated in the NcNc and the CNc condition. The visibility of the low-contrast target was significantly lower than the high-contrast target.

On the other hand, there was no significant correlation between the d’ and the rates of correct response in the FC task [NcNc: r = 0.19, t(16) = 0.78, p > .100; NcC: r = 0.11, t(16) = 0.46, p > .100; CNc: r = 0.20, t(16) = 0.82, p > .100; CC: r = 0.05, t (16) = 0.19, p > .100]. The one way ANOVA indicated that the main effect of the T1 contrast was significant [F(2.34, 39.84) = 675.58, p < .001, η2 = 0.96]. Multiple comparisons using a Holm's sequentially rejective Bonferroni procedure, there was a significant difference between the condition presenting the low contrast T1 and the high contrast T1 [NcNc vs CC: t(17) = 30.74, p < .001; NcC vs CC: t(17) = 29.88, p < .001; NcNc vs CNc: t(17) = 29.40, p < .001; NcC vs CNc: t(17) = 25.58, p < .001]. There were no significant differences between conditions that the same contrast T1 was presented: the NcNc and the NcC condition [t (17) = 0.87, p > .100], the CNc and the CC condition [t(17) = 1.90, p > .100]. The mean d' of the T2 was 0.26 (SD = 0.45) in the NcNc, 3.59 (SD = 0.55) in the NcC, 0.55 (SD = 0.52) in the CNc, and 3.79 (SD = 0.30) in the CC (Fig. 2B). Similarly to the T1, the d' of the T2 was significantly different from zero in the all conditions [NcNc: t (17) = 2.42, p < 0.001; NcC: t(17) = 27.61, p < .001; CNc: t(17) = 4.41, p < .001; CC: t(17) = 53.11, p < .001], and there was no significant correlation between rates of correct response in the FC task [NcNc: r = 0.26, t(16) = 1.08, p > .100; NcC: r = -0.11, t (16) = -0.42, p > .100; CNc: r = 0.43, t(16) = 1.91, p < .010; CC: r = 0.26, t(16) = 1.06, p > .100]. These results indicated that participants could see the target stimulus consciously in a few trials, but such awareness regarding the reports of each target were directly influenced by the FC task accuracy. The main effect of the T2 contrast was significant [F(2.2, 37.41) = 337.34, p < .001, η2 = 0.93]. There were significant differences between the condition presenting the low contrast T2 and the high contrast T2 [NcNc vs CC: t(17) = 23.02, p < .001; CNc vs CC: t(17) = 21.86, p < .001; NcNc vs NcC: t(17) = 19.20, p < .001; NcC vs CNc: t (17) = 17.32, p < .001], the NcNc and the CNc was a significant difference [t(17) = 2.28, p < .050]. There was also a difference between the NcC and the CC condition [t(17) = 2.62, p < .050]. In the following results, trials that participants reported “seen” for the low contrast target (visibility rating scores 3 & 4) and “unseen” for the high contrast target (visibility rating scores 1 & 2) were removed from the analysis of the FC performance (Fig. 3). The mean rates of correct responses of the FC task were significantly above the chance level [50%, Wilcoxon rank sum test, NcNc: W = 279, p < .001 (mean = 0.60, SD = 0.09); NcC: W = 288, p < .001 (mean = 0.62, SD = 0.14); CNc: W = 324, p < .001 (mean = 0.78, SD = 0.14); CC: W = 324, p < .001 (mean = 0.99, SD = 0.02)]. These data were arcsine transformed before being submitted to an ANOVA. The 2 way ANOVA indicated that there were significant main effects for the T1 contrast [F(1, 17) = 234.97, p < .001, η2 = 0.52] and the T2 contrast [F(1, 17) = 76.98, p < .001, η2 = 0.15]. There was a significant interaction between the T1 and T2 contrast conditions [F(1, 17) = 34.00, p < .001, η2 = 0.12]. Analyses of simple effects for this interaction indicated that the rate of correct responses for the NcNc condition was significantly different from that for the CNc condition [F(1, 17) = 22.38, p < .001, η2 = 0.34], while there was no significant difference between the NcNc and the NcC conditions [F(1, 17) = 0.85,

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Consciousness and Cognition 78 (2020) 102859

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Fig. 3. The mean rates of correct responses in the FC task. Error bars represented SEM. Participants were instructed to guess the spatial location of each target presentation and had to select whether two target stimuli were presented in the same position or not. The visibility score 1 and 2 were labeled as unconscious trials, score 3 and 4 were labeled as conscious trials. The mean rates of correct responses were above the chance level (50%) in all conditions. There was no significant difference between the NcNc and the NcC.

p > .100, η2 = 0.01]. The rate of correct responses for the CC condition was significantly higher than that for the CNc condition [F (1, 17) = 66.77, p < .001, η2 = 0.67] and for the NcC condition [F(1, 17) = 232.65, p < .001, η2 = 0.87]. The mean RTs of the FC task were showed in Fig. 4 [NcNc: 576.62 ms (SD = 140.50); NcC: mean = 534.54 ms (SD = 132.92); CNc: mean = 556.12 ms (SD = 131.65); CC: mean = 400.96 ms (SD = 94.97); Control: mean = 575.41 ms (SD = 141.51)]. Analyses revealed significant main effects for the T1 contrast [F(1, 17) = 16.03, p < .001, η2 = 0.08]and for the T2 contrast [F(1, 17) = 35.52, p < .001, η2 = 0.12]. There was a significant interaction [F(1, 17) = 35.52, p < .001, η2 = 0.04]. The simple effects for this interaction indicated that the RT for the CC condition was faster than that for the CNc [F(1, 17) = 41.33, p < .001, η2 = 0.33] and for the NcC [F(1, 17) = 26.58, p < .001, η2 = 0.26]. There was no significant difference between the NcNc and the CNc [F(1, 17) = 0.64, p > .100, η2 = 0.01] and a marginal difference between the NcNc and the NcC [F(1, 17) = 3.20, p < .100, η2 = 0.02]. For the control condition, there were no significant differences between the control condition and the NcNc [t (34) = 0.02, p > .100]; the NcC [t(34) = -0.90, p > .100], and the CNc [t(34) = -0.42, p > .100]. The RT for the CC condition was faster than that for the control condition [t(34) = -4.34, p < .001]. For the additional analyses, the mean rates of correct responses of the FC task were re-computed that rejecting trials which scored 2, 3, and 4 for the low contrast target in the visibility rating task (Fig. 5). The CC and CNc conditions were above the chance level [50%, Wilcoxon rank sum test, CNc: W = 261, p < .001 (mean = 0.77, SD = 0.20); CC: W = 306, p < .001 (mean = 0.99, SD = 0.01)]. The NcC was marginally above the chance level [W = 198, p < .100 (mean = 0.54, SD = 0.10)], however no significant difference between the NcNc and the chance level [W = 180, p > .100 (mean = 0.49, SD = 0.27)]. The 2 way ANOVA indicated that there were significant main effects for the T1 contrast [F(1, 15) = 97.14, p < .001, η2 = 0.50] and the T2 contrast [F (1, 15) = 16.93, p < .010, η2 = 0.10]. There was a significant interaction between the T1 and T2 contrast conditions [F(1, 15) = 15.78, p < .010, η2 = 0.07]. Analyses of simple effects for this interaction indicated that the rate of correct responses for the NcNc condition was significantly different from that for the CNc condition [F(1, 15) = 11.21, p < .010, η2 = 0.25], while there was no significant difference between the NcNc and the NcC conditions [F(1, 15) = 0.25, p > .100, η2 = 0.01]. The rate of correct responses for the CC condition was significantly higher than that for the CNc condition [F(1, 15) = 40.02, p < .001, η2 = 0.55] and for the NcC condition [F(1, 15) = 531.32, p < .001, η2 = 0.25].

Fig. 4. The mean RTs in the FC task. Error bars represented SEM. Participants had to react as fast as they can in the FC task. The RT in the CC condition was significantly faster than other conditions. There were no significant differences between the control condition and the NcNc, the NcC, and the CNc condition. 6

Consciousness and Cognition 78 (2020) 102859

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Fig. 5. The mean rates of correct responses in the FC task. Error bars represent SEM. Participants were instructed to guess the spatial location of the presentation of each target and they had to select whether or not two target stimuli were presented in the same position. The visibility score 1 was labeled as unconscious trials, the scores 2, 3, and 4 as conscious trials. The NcC condition was marginally above the chance level (50%) but the NcNc was not different from it.

4. Discussion The present study aimed to clarify whether two unconscious visual information could be compared to each other. The overall performance was above chance level in all conditions under the FC task and no difference between the NcNc and NcC conditions was found. Our results showed that the visuo-spatial information is stored without visual conscious experience, and the information is also operated at the stage of comparing process under the delayed match-to-sample task. These results indicate that participants were capable to respond correctly to the invisible low-contrast target and suggest that the goal-directed behavior, that includes the comparing process, could be mediated unconsciously by the central executive control known as Baddeley's working memory model (Baddeley, 2003). 4.1. Changing strategy when the conscious T1 was presented In the condition where the conscious visual information was presented first in the trial (the CNc and the CC), the accuracy of the FC task was significantly higher than in the condition where the unconscious information was presented first. In the present study, the masking effect was controlled by the luminance contrast of the target stimuli. The high contrast target itself, will be easily detected compared to the low contrast target. We used this low contrast target as the unconscious one. In addition to that, the visual attention is depended on the physical condition of the visual stimulus (Itti, Koch, & Niebur, 1998). When the contrast of T1 was high enough and detected easily, the spatial attention would be oriented to the spatial location of the T1. According to the recent model about the relationship between the executive function and consciousness, conscious information can create a new goal for the task and plan for executing the task-related action, but unconscious information cannot (Ansorge et al., 2014). There are commonalities between this model and our findings. The conscious T1 could activate the creation of a new strategy for the task by the executive function and it could induce a high precision response. In particular, when the participants judged whether the target stimulus existed at the spatial location where their attention was oriented by the conscious T1, this judgment would be easier than detecting one location from four alternative locations. The change of strategy for the task resulted in the difference between the accuracy of the conscious T1 (the NcNc and the NcC) and the unconscious T1 condition (the CNc and the CC). This suggests that the executive model of Ansorge et al. (2014) does not only explain the priming but could also be adapted to goal-directed behavior. 4.2. Execution process without visual consciousness In the condition that the unconscious visual information was presented first in the trial (the NcNc and the NcC), the accuracy of the FC task was not affected by whether the second stimulus was conscious or unconscious. This suggests that the task execution is unconscious and is independent of the visual conscious experience of the visual stimulus that is necessary for executing the task. The neural model of consciousness explains that the neural network consists of a local network and a global network. The visual consciousness depends on the visual information accessing the global network (Baars, 1997; Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006; Dehaene & Naccache, 2001). The main neural basis of the executive function is involved in the frontal regions (Mazoyer et al., 2001) and that of the visual perceptual processing is in the occipital regions. The visual information, which is supposed to drive the executive function, requires the global network to access consciousness because these regions are anatomically the other side of the brain. Based on this model, the performance under the condition that contains the conscious visual item will be better (compared to the condition containing the unconscious items) since the consciousness of the visual evidence for executing the task would help the task execution. But our results were not the case: No significant difference was observed between the NcNc and the NcC in the present study. This indicates that the visual consciousness would not affect the execution of the delayed-match-tosample task, suggesting that the executive function for the task was sufficiently activated by the unconscious visual items. This 7

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supports the argument of the previous study that the visual working memory is unconsciously processed (Soto et al., 2011). In addition to that, there is the possibility that the visual information is maintained unconsciously. The visual information cannot access the central executive directly and it will be stored at the visuo-spatial sketchpad (Baddeley, 2012). If the visual consciousness does not affect the access to the central executive, the visuo-spatial sketchpad which is the via point will also be unconscious. Although, there is not enough conclusive proof of this argument from the results of the present study. In the present study, we rather applied the lenient baseline to categorize the conscious/ unconscious trials compared to that used in other recent studies. This study focused on only “visual” consciousness, thus the subjective visibility rating classified the conscious and unconscious trials based on whether the visual awareness was reported or not. In the FC task analysis, the score 2 of the visibility rating, “did not see the target but felt the existence of something”, was categorized as the unconscious trial. In the result, the score 2 rating for the low contrast target was observed. The previous blindsight study reported that the blindsight patients selected the score 2 of the PAS rating for the visual stimulus presented at the blind visual field and, suggested that such type of awareness report is related to the type-2 blindsight like awareness (Mazzi, Bagattini, & Savazzi, 2016). The type-2 blindsight is the phenomenon that some blindsight patients report conscious awareness for a visual input in the visual field defected by cortical blindness (Zeki & Ffytche, 1998). Although our experiment was conducted with participants who have normal vision, it is conceivable that the score 2 (“did not see the target but felt the existence of something”) in the visibility rating task was chosen as the score which represents that they did not experience visual consciousness concerning the target. This could have occurred as non-visual phenomenal consciousness that is akin to the type-2 blindsight. In the present study, we operationally define such a phenomenon as “non-visual awareness” of the visual information. It means, that although the given visual target is still below the threshold level for a subjective visual conscious report [the score 3 (“saw the target but it was not clear”) and 4 (“saw the target clearly”)] the target is good enough to exceed the threshold for a subjective non-visual conscious report, resulting in choosing the score 2. Additional analyses, with rejected trials, in which participants reported the score 2 for the visibility rating for masked target stimuli, showed that the rate of correct responses in the NcNc condition was not above chance level. The different results observed in the NcNc condition, which are depending on whether the score 2 was fed into analysis or not, could be interpreted as the effect of the non-visual awareness of the working memory. Our results may imply that the visual consciousness did not relate the working memory but the non-visual awareness was required to access the central executive although the number of trials was still not sufficient to discuss this possibility. In addition, it would be interesting for us to take a look at the experiments of a recent study which separated the participants’ task into two phases: these are (1) the study phase (animacy judgment) and (2) the test phase (recognition task by judging whether the target was in the study phase or not). The result of the recognition task with the unconscious visual stimulus indicated that the participants’ performance was above the chance level (Chong et al., 2014), suggesting the existence of unconscious visual recognition memory. In their other experiments 3 and 4, on the other hand, the animacy judgment for the unconscious visual cue indicated that the performance was not significantly different from the chance-level. Chong et al. argued the characteristic of conscious/unconscious visual memory in such a way that the semantic encoding is strongly associated with conscious memory whereas it could not be easily deployed by means of the visual masking paradigm. Similarly, in the present study, the unconscious visual information could not be deployed from the visuo-spatial sketchpad to the central executive and such an inhibition by the masking would lead to a degradation of the performance. There is a possibility that non-visual awareness would support deploying visual information without visual consciousness for executing the experimental task. Although, functional differences in visual and non-visual awareness for the visual stimulus is still unclear. Other types of experimental methods to measure awareness of the visual stimulus (e.g., confidence rating, post-decision wagering) also cannot classify with dissociating the other sense, or the multi-sense, and the visual awareness. Further studies would be required to discuss the relationship between the working memory and the type of awareness for executing the task, and how to measure and classify types of awareness. At first glance, our results can be interpreted as such that the “visual” conscious experience does not directly lead the flexibility of the executive function. Although it has been explained that some cognitive processes (e.g., selective attention) are necessary for accessing consciousness (Dehaene et al., 2006), it could also be possible that such cognitive processes serve as a gatekeeper of the consciousness and intermediate the flexibility of the executive function. Our results only suggest that accessing visual consciousness and the executive function are independent processes, and thus we conclude that it is not always necessary to access the visual consciousness to activate the executive function. Because recent studies suggested that several visual processes are needed to access visual consciousness (Cox, Sperandio, Laycock, & Chouinard, 2018; Ramey, Yonelinas, & Henderson, 2019), it is important to further examine in detail what kind of experimental task requires accessing visual consciousness to clarify the need for visual consciousness. The neural activity which assumes the executive function would depend on a neural pathway which does not via the global pathway. The basic visual neural pathway is composed of a connection from the retina to the primary visual area in the occipital cortex via the lateral geniculate nuclei (Carandini, 2012). On the other hand, another visual pathway, which does not pass through the lateral geniculate body but originates from the retina to the superior colliculus, also exists and this pathway is connected to the frontal regions (Liddell et al., 2005; Tamietto & De Gelder, 2010). This subcortical visual pathway relates eye movement (Isa & Yoshida, 2009), action (Danckert & Rossetti, 2005), emotion (Liddell et al., 2005), and blindsight (Tamietto & Morrone, 2016). The executive function which is driven by frontal neural activity would be driven through the subcortical pathway. The results of our study may be interpreted in a way that the execution would be mediated by such neural activities. A study using monkeys indicated that the neural activity of the superior colliculus, which is the neuro-anatomical structure of the subcortical pathway, is affected by learning (Takaura, Yoshida, & Isa, 2011). From pieces of evidence from previous studies, it is quite likely that the subcortical visual pathway serves as a bypath to the frontal regions and fulfills the functional role of underlying bases to execute a wide range of activities concerning unconscious visual inputs. To figure out the overall picture of the relationship between brain activity and consciousness, it would be important to focus on the subcortical activity in addition to the cortical network. 8

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4.3. Capability of awareness measurement in the RTs The results also showed that the pattern of the correct responses and that of the RTs appeared to be different from each other among the experimental conditions (Figs. 3 & 4). The RT of the CC condition was faster compared to the other conditions, but there were no significant differences between the control condition and conditions with the unconscious target (the NcNc, NcC, & CNc). Generally, the RT tends to be fast when participants had high confidence in the response, and vice versa (Robinson, Johnson, & Herndon, 1997). This suggests that the confidence for the forced choice response could be only high when both of the two visual items (T1 & T2) were consciously detected. With respect to the functional relationship between the RT and the response confidence, the confidence in the response may depend on the awareness of the key information in a given task. And this could be utilized for some indirect awareness measures such as the confidence rating (Cheesman & Merikle, 1986) and the post decision wagering (Persaud, McLeod, & Cowey, 2007). From these viewpoints, there might be a possibility that differences in the RTs of the FC task indirectly reflected participants’ awareness about the target stimuli. Hence, results of RTs support our claim that the unconscious visual information increases the performance of the experimental task involved in the visual working memory. 4.4. Limitations of this study Our study verified the functional effect of the visual conscious awareness for the visual working memory activity. For the results of subjective measurement, the awareness for the target stimuli rated by the visibility rating showed that d' for the low contrast target was higher than that for the high contrast target (Fig. 2). This means that the masking stimuli worked to distract the awareness of the target stimulus. On the other hand, the d' for the low contrast target was significantly different from zero. Although these results mean that participants are aware of the existence of the target stimulus in a few trials, it should also be considered that these above chancelevel performances in the FC task did not depend on the awareness concerning the target because of the following two reasons: First, there were no significant correlations between the rate of correct responses and “seen” responses by the visibility rating. Second, the rate of correct responses was computed after removing trials which were rated as “seen” responses for the low contrast target presentation from the analysis. Hence the rate of correct responses in the FC task was not affected directly by the target stimulus. It would be possible that the above chance-level performance is caused by the unconscious visual input. The problematic issue of our experiment is that the number of trials was not enough to analyze functional differences between the trial scored visibility rates. In our additional analyses of the forced-choice task, over 50% of the trials (13 trials on average) were removed from the analyses in the NcNc condition. An additional experiment with an increased number of trials in each condition will allow us to minimize the influence of removed trials in which participants reported awareness of the target stimulus. This may be necessary to define a strict baseline. The issue whether the non-visual awareness of the visual stimulus is required to activate the executive function system is still unsolved. The working memory model has indicated that visual information can be recorded verbally and then gain access to the phonological loop through a rehearsal (e.g., Baddeley, 2003). The present study cannot completely reject the possibility that the unconscious visual input is converted into auditory information. Unconscious visual input could be stored consciously in the phonological loop, and therefore the participants report an unconscious awareness in the trials. It seems to be reasonable to conclude that at least the “visual” conscious experience is not involved in executing the present experimental task, although further research would be required to discuss whether the information from the other sensory modalities besides visual information could have an impact on the function of the visual working memory for executing the experimental task. 5. Conclusions In summary, the present results lead us to conclude that the executive function which is involved with the central executive of the working memory could be driven without accessing visual consciousness about visual stimuli at least. However, it is possible that non-visual awareness about the visual stimuli (which is below the threshold level for the subjective visual conscious report, e.g., “saw the stimulus”, but good enough to exceed the threshold for the report, e.g., “felt the existence of something”) is necessary to activate the executive function. It goes without saying that the goal-directed behavior in our daily life needs the working memory, but the results of the present study imply that the behavior could be prepared and executed via an unconscious process. However, the reason why we need to experience the visual world consciously is still unclear. Further studies are necessary to clarify the functional role of consciousness and to answer the question why we see the world consciously. CRediT authorship contribution statement Shun Nakano: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Writing original draft, Visualization. Masami Ishihara: Conceptualization, Investigation, Resources, Writing - review & editing, Supervision, Project administration, Funding acquisition. Acknowledgements This work was supported by JSPS KAKENHI Grant Numbers JP26380992 and JP25242060. The authors wish to thank Kuniyasu Imanaka, Hidemi Komatsu, Hayaki Banno, and our laboratory colleagues for their helpful comments on this work. 9

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