Explaining the SPoARC and SNARC effects with knowledge structures: An expertise account

Spatial-positional associations in short-term memory can vanish in long-term memory

Studies on the SPoARC effect have shown that serial information is spatially processed in working memory. However, it remains unknown whether these spatial-positional associations are durable or only temporary. This study aimed at investigating whether spatialization would persist when a sequence presented repeatedly is expected to be chunked. If chunked, the items could be unified spatially and their spatialization could vanish. Thirty-seven participants performed a spatialization task which was remotely inspired by the Hebb repetition paradigm. A sequence of four stimuli presented individually in the middle of a computer screen was repeated throughout the task. After each sequence, participants had to decide whether a probe belonged to the series using two lateralized response keys. The results showed no spatialization for these repetitive sequences, on average. Moreover, further analysis revealed that the effect was detectable at the beginning of the task, suggesting that the more the sequence was repeated, the less participants spatialized information from left to right. These findings show that associations created in working memory between items and space can vanish in repeated sequences: we discuss the idea that working memory progressively saves on spatialization once a sequence is chunked in long-term memory.

Inhibition and working memory capacity modulate the mental space-time association

This research aimed to investigate whether the mental space-time association of temporal concepts could be modulated by the availability of cognitive resources (in terms of working memory and inhibitory control capacities) and to explore whether access to this association could be an automatic process. To achieve this, two experiments were carried out. In Experiment 1, participants had to classify words with future and past meanings. The working memory load (high vs. low) was manipulated and the participants were grouped into quartiles according to their visuospatial working memory capacity (WMC). Temporal concepts were displayed subliminally (immediate masking) and supraliminally (delayed masking). The ANOVA showed a performance pattern consistent with the left-past right-future conceptual scheme, regardless of both the type of masking and the working memory load, except in high WMC participants, in which, interestingly, the space-time association effect was absent. In Experiment 2, participants were asked to respond to the colour of the font of the temporal words, and their attentional control capacity was assessed. The results indicated a timeline effect that was irrespective of the WM load and the type of perceptual processing, but not of the WM capacity or the inhibitory abilities. These findings partially endorse the automatic and implicit access to the mental space-time association and suggest the involvement of the availability of cognitive resources. Individual WMC differences appear to modulate the automatic nature of the effect rather than the processing conditions themselves.

Influence of different spatial representations on the SNARC effect for letters: Electrophysiological evidence

Studies have previously demonstrated that different spatial representations may affect the spatial-numerical association of response codes (SNARC) effect for numbers; however, limited studies have assessed the SNARC effect for letters. In this study, event-related potentials (ERPs) were used to measure the influence of two spatial representation modes (ruler and clock) on the SNARC effect. The ruler produced a SNARC-like effect; i.e., the left hand reacted faster than the right to the letters that appeared before N in the alphabet; the right hand reacted faster than the left to the letters that appeared after N, whereas the clock produced a reverse SNARC effect. In addition, the ERP data showed that the SNARC-like effect for letters in both representations induced significant activation in the frontal and parietal regions, indicating that the same brain areas are involved in processing letters and numbers in terms of spatial dimensions. This study further identified the conditions for the SNARC effect and proved that the SNARC effect is attributed to the simultaneous participation of brain regions for sequence and spatial information processing.

Optimized experimental designs to best detect spatial positional association of response codes in working memory

The SPoARC (Spatial Positional Association of Response Codes) effect refers to spatialization of information in working memory. Among the potential factors that could influence how order is mapped onto a mental space during the recognition process, we selected the following two factors: i) the type of stimuli, in particular their verbal vs. visual aspects and ii) the number of probes. In this study, 137 participants memorized sequences of either words or pictures and subsequently performed a recognition test for which they responded using lateralized keys. For half of the participants, only one probe was presented after each sequence, whereas the other half was administered several probes. A significantly greater number of participants presented a SPoARC using a single probe. We discuss that spatialization is best detected when the sequence is scanned only once. Results also showed no difference between the two types of stimuli (i.e., verbal vs. visual). This finding raises the question of the respective roles of verbalization and visualization in the SPoARC.

The role of cognitive control in the SNARC effect: A review

The spatial-numerical association of response codes (SNARC) effect, in which people respond to small numbers faster with the left hand and to large numbers faster with the right hand, is a popular topic in cognitive psychology. Some well-known theoretical accounts explaining this effect include the mental number line model, polarity correspondence principle, dual-route model, and working memory account. However, these fail to explain the finding that the size of the SNARC effect is modulated by cognitive control. Here, we propose a new account-a cognitive control-based view of the SNARC effect. This view argues that the SNARC effect is fundamentally determined by cognitive control in resolving conflicts during stimulus-response mapping. Several subcomponents of cognitive control, such as working memory, mental or task set shifting, inhibition control, and conflict adaptation, can easily modulate the SNARC effect. The cognitive control-based view can account for the flexible SNARC effect observed in diverse task situations while providing new insight into its mechanism.

A SPoARC of Music: Musicians Spatialize Melodies but not All-Comers

Recent studies on the spatial positional associated response codes (SPoARC) effect have shown that when Western adults are asked to keep in mind sequences of verbal items, they mentally spatialize them along the horizontal axis, with the initial items being associated with the left and the last items being associated with the right. The origin of this mental line is still debated, but it has been theorized that it necessitates specific spatial cognitive structures to emerge, which are built through expertise. This hypothesis is examined by testing for the first time whether Western individuals spatialize melodies from left to right and whether expertise in the musical domain is necessary for this effect to emerge. Two groups (musicians and non-musicians) of participants were asked to memorize sequences of four musical notes and to indicate if a subsequent probe was part of the sequence by pressing a "yes" key or a "no" key with the left or right index finger. Left/right-hand key assignment was reversed at mid-experiment. The results showed a SPoARC effect only for the group of musicians. Moreover, no association between pitch and hand responses was observed in either of the two groups. These findings suggest a crucial role of expertise in the SPoARC effect.

Neural Patterns in Parietal Cortex and Hippocampus Distinguish Retrieval of Start versus End Positions in Working Memory

Coding serial order of information is a fundamental ability of our cognitive system, and still, little is known about its neural substrate. This study examined the neural substrates involved in the retrieval of information that is serially stored in verbal working memory task using a sensitive multivariate analysis approach. We compared neural activity for memorized items stemming from the beginning versus the end of a memory list assessing the degree of neural pattern discordance between order positions (beginning vs. end). The present results confirmed and refined the role of the intraparietal sulcus in the processing of serial order information in working memory. An important finding is that the hippocampus showed sensitivity to serial order information. Our results indicate that the representation of serial order information relies on a broader set of neural areas and highlight the role of the intraparietal sulcus and the hippocampus, in addition to the supramarginal gyrus and the SMA. The contribution of different neural regions might reflect the involvement of distinct levels of serial order coding (i.e., spatial, attentional, temporal) that support the representation of serial order information.

Eye-movements reveal the serial position of the attended item in verbal working memory

The problem of how the mind can retain sequentially organized information has a long research tradition that remains unresolved. While various computational models propose a mechanism of binding serial order information to position markers, the representational nature and processes that operate on these position markers are not clear. Recent behavioral work suggests that space is used to mark positions in serial order and that this process is governed by spatial attention. Based on the assumption that brain areas controlling spatial attention are also involved in saccadic planning, we continuously tracked the eye-movements as a direct measure of the spatial attention during retrieval from a verbal WM sequence. Participants memorized a sequence of auditory numbers. During retention, they heard a number-cue that did or did not belong to the memorized set. After this number-cue, a target-beep could be presented to which they had to respond if the number-cue belonged to the memorized sequence. In Experiment 1, the target-beep was either presented to the left or right ear, and in Experiment 2 bilaterally (removing any spatial aspect). We tested the hypothesis that systematic eye-movements are made when people retrieve items of sequences of auditory words and found that the retrieval of begin items resulted in leftward eye-movements and the retrieval of end items in rightward eye-movements. These observations indicate that the oculomotor system is also involved in the serial order processes in verbal WM thereby providing a promising novel approach to get insight into abstract cognitive processes.

Early is left and up: Saccadic responses reveal horizontal and vertical spatial associations of serial order in working memory

Maintaining serial order in working memory is crucial for cognition. Recent theories propose that serial information is achieved by positional coding of items on a spatial frame of reference. In line with this, an early-left and late-right spatial-positional association of response code (SPoARC) effect has been established. Various theoretical accounts have been put forward to explain the SPoARC effect (the mental whiteboard hypothesis, conceptual metaphor theory, polarity correspondence, or the indirect spatial-numerical association effect). Crucially, while all these accounts predict a left-to-right orientation of the SPoARC effect, they make different predictions regarding the direction of a possible vertical SPoARC effect. In this study, we therefore investigated SPoARC effects along the horizontal and vertical spatial dimension by means of saccadic responses. We replicated the left-to-right horizontal SPoARC effect and established for the first time an up-to-down vertical SPoARC effect. The direction of the vertical SPoARC effect was in contrast to that predicted by metaphor theory, polarity correspondence, or by the indirect spatial-numerical association effect. Rather, our results support the mental whiteboard-hypothesis, according to which positions can be flexibly coded on an internal space depending on the task demands. We also found that the strengths of the horizontal and vertical SPoARC effects were correlated, showing that some people are more prone than others to use spatial references for position coding. Our results therefore suggest that context templates used for position marking are not necessarily spatial in nature but depend on individual strategy preferences.

Interaction mechanism between location and sequence in letter cognition

A previous study used days as a sequence symbol to investigate the interaction mechanism between location and sequence in sequence symbol cognition; the study findings suggested that the spatial stimulus-response compatibility effect and the Simon effect could not co-exist with the SNARC-like effect when processing sequence symbols. The previous study did not include the influence of the difficulty of identifying sequence symbols on the Simon effect in the investigation, so it is unclear whether the conclusion about processing sequence symbols with considerable identification difficulty can be extended to the processing of sequence symbols with less identification difficulty. Therefore, the present study explored letters that have a low level of identification difficulty to investigate the interaction mechanism between location and sequence in sequence symbol cognition. Participants were asked to classify a probe letter, which was randomly displayed on the left or right side of the screen, according to its location (Experiment 1), its sequence (Experiment 2) or its colour (Experiment 3). The results indicated that (1) only the spatial stimulus-response compatibility effect and Simon effect were present in the letter location classification task and letter colour classification task, respectively. (2) The Simon effect co-existed with the SNARC-like effect, and these two effects interacted with each other in the letter sequence classification task. From these results, it can be concluded that the task determines whether the Simon effect and the SNARC-like effect can co-exist, with differences presented across sequence symbols.

Using space to remember: Short-term spatial structure spontaneously improves working memory

Spatial information plays an important role in how we remember. In general, there are two (non mutually exclusive) views regarding the role that space plays in memory. One view is that objects overlapping in space interfere with each other in memory. For example, objects presented in the same location (at different points in time) are more frequently confused with one another than objects that are not. Another view is that spatial information can 'bootstrap' other kinds of information. For example, remembering a phone number is easier one can see the arrangement of a keypad. Here, building on both perspectives, we test the hypothesis that task-irrelevant spatial structure (i.e., objects appearing in stable locations over repeated iterations) improves working memory. Across 7 experiments, we demonstrate that (1) irrelevant spatial structure improves memory for sequences of objects; (2) this effect does not depend on long-term spatial associations; (3) this effect is unique to space (as opposed to features like color); and (4) spatial structure can be teased apart from spatial interference, and the former drives memory improvement. We discuss how these findings relate to and challenge 'spatial interference' accounts as well as 'visuospatial bootstrapping'.

The neural mechanism of spatial-positional association in working memory: A fMRI study

In the last decade, research has reported that items at the beginning of a memorized sequence are responded to faster with the left hand, whereas items at the end are responded to faster with the right hand. This Spatial-Positional Associations of Response Codes effect has been extensively studied using behavioral methods. However, the neural networks underlying it remain unclear. We found using functional magnetic resonance imaging (fMRI) that the dorsal attention network was involved in spatial-positional associations, in particular a region of the right superior frontal cortex / pre-supplementary motor area (pre-SMA), within which neural activity correlated with behavioral measures of the strength of spatial-positional associations. Psychophysiological interaction (PPI) analysis revealed functional connectivity between this area and other regions of the dorsal attentional network including the SMA, and with the hippocampal-retrosplenial network. In contrast, explicit processing of serial order independent of spatial-positional associations was related to activity in the inferior parietal cortex. Our results provide new insight into positional coding theories of working memory, including the mental whiteboard hypothesis. They suggest that the behavioral effects of positional coding (congruency between hand and ordinal position within the list) are mediated through spatial and motor control maps in the dorsal attentional system.

Bootstrapping the visuospatial bootstrapping effect and testing its spatialisation

When sequences of digits are visually presented within a numerical keypad on a screen, memory span increases, this effect was named visuospatial bootstrapping. The aim of the first experiment was to know if this effect could emerge without presenting a keypad on the screen. For this purpose, a three-phase experiment was designed. During phase 1, the immediate serial recall of two groups of participants was compared (pre-training): the first group saw sequences of one-digit numbers displayed on a screen within a keypad (the keypad group) whereas the second group heard the (same) sequences (the auditive group). During phase 2, all participants underwent a training session to help them visualise in their mind a keypad. Finally, in the third phase, participants were tested again with an immediate serial recall task (post-training). Results showed that both groups had comparable performance in post-training indicating that the visuospatial bootstrapping could be obtained without displaying a numerical keypad. The second experiment also involved a keypad group and an auditive group and was designed to investigate their spatial representation. Results showed that both groups spatialised the digits following the keypad spatial configuration: digits 1-4-7 were associated to left, 2-5-8 to middle and 3-6-9 to right.

Spatialization in working memory: can individuals reverse the cultural direction of their thoughts?

A recent study based on the SPoARC effect (spatial position association response codes) showed that culture heavily shapes cognition and more specifically the way thought is organized; when Western adults are asked to keep in mind a sequence of colors, they mentally organize them from left to right, whereas right-to-left reading/writing adults spatialize them in the opposite direction. Here, we investigate if the spontaneous direction of spatialization in Westerners can be reversed. Lists of five consonants were presented auditorily at a rate of 3 s per item, participants were asked to mentally organize the memoranda from right to left. Each list was followed by a probe. Participants had to indicate whether the probe was part of the sequence by pressing a "yes" key or a "no" key with the left or right index finger. Left/right-hand key assignment was switched after half of the trials were completed. The results showed a reverse SPoARC effect that was comparable in magnitude to the spontaneous left-to-right SPoARC effect found in a previous study. Overall, our results suggest that individuals can reverse the cultural direction of their thoughts.

A purely power-space association without spatial and strategic biases

Previous studies have shown that powerful and powerless concepts are metaphorically associated with top and bottom spaces respectively. However, this association might be contaminated by spatial and strategic biases due to the involvement of spatialized stimuli or responses. It is unknown whether power by itself can automatically activate spatial representations. To eliminate spatial and strategic biases, Experiment 1 separately presented power and spatial stimuli at the center of the screen, and participants had to classify power words and HIGH/LOW labels (Experiment 1a) or indicate up/down arrows (Experiment 1b) using a single key and follow different response rules that were combined with a Go/no-go task. Experiment 2 replicated the non-spatialized design but used an implicit power judgment task. Based upon the non-spatialized method, the results provide the first evidence that a power-space association effect still exists when eliminating spatial and strategic biases, revealing the nonconscious spatial nature of power.

The development of working memory spatialization revealed by using the cave paradigm in a two-alternative spatial choice

When Western participants are asked to keep in mind a sequence of verbal items, they tend to associate the first items to the left and the last items to the right. This phenomenon, known as the spatial-positional association response codes effect, has been interpreted as showing that individuals spatialize the memoranda by creating a left-to-right mental line with them. One important gap in our knowledge concerns the development of this phenomenon: when do Western individuals start organizing their thought from left to right? To answer this question, 274 participants in seven age groups were tested (kindergarten, Grades 1, 2, 3, 4, and 5, and adults). We used a new protocol meant to be child-friendly, which involves associating two caves with two animals using a two-alternative spatial forced choice. Participants had to guess in which cave a specific animal could be hidden. Results showed that it is from Grade 3 on that participants spatialize information in working memory in a left-to-right fashion like adults.

Exploring the interactions among SNARC effect, finger counting direction and embodied cognition

The Spatial Numerical Association of Response Code (SNARC) is the preferential association between smaller/larger magnitudes and left/right side, respectively. Some evidence suggest a link between SNARC and a left-to-right finger counting habit. We asked 268 participants to show how they use the hands to count from 1 to 10. By means of this ecological task, 80% of the sample use first the right hand (to count from 1 to 5) and the majority of them use a palm-up posture. In Experiment 2 (N = 46) right-starters were asked to categorize 1-to-5 magnitudes as even or odd, using the left and right hand. Stimuli were presented both as Arabic numbers and by means of left and right hand photographs in palm-up and palm-down posture. Results confirmed the expected SNARC effect in the Arabic condition. With hand images we found that right hand responses were better for larger than for smaller magnitudes (SNARC, mainly for left hand palm-up stimuli), showing that the SNARC can be generalized to different codes. Finally, the interactions between magnitudes and left/right hand images in palm-up and palm-down posture suggest that embodied cognition can influence numerical processing.

Spatial complexity facilitates ordinal mapping with a novel symbol set

The representation of number symbols is assumed to be unique, and not shared with other ordinal sequences. However, little research has examined if this is the case, or whether properties of symbols (such as spatial complexity) affect ordinal learning. Two studies were conducted to investigate if the property of spatial complexity affects learning ordinal sequences. In Study 1, 46 adults made a series of judgements about two novel symbol sets (Gibson and Sunúz). The goal was to find a novel symbol set that could be ordered by spatial complexity. In Study 2, 84 adults learned to order nine novel symbols (Sunúz) with a paired comparison task, judging which symbol was 'larger' (whereby the larger symbol became physically larger as feedback), and were then asked to rank the symbols. Participants were assigned to either a condition where there was a relationship between spatial complexity and symbol order, or a condition where there was a random relationship. Of interest was whether learning an ordered list of symbols would be facilitated by the spatial complexity of the novel symbols. Findings suggest spatial complexity affected learning ability, and that pairing spatial complexity with relational information can facilitate learning ordinal sequences. This suggests that the implicit cognitive representation of number may be a more general feature of ordinal lists, and not exclusive to number per se.