Operational Momentum During Ordering Operations for Size and Number in 4-Month-Old Infants

An Operational Momentum (OM) effect is shown by 9-month-old infants during non-symbolic arithmetic, whereby they overestimate the outcomes to addition problems, and underestimate the outcomes to subtraction problems. Recent evidence has shown that this effect extends to ordering operations for size-based sequences in 12-month-olds. Here we provide evidence that OM occurs for ordering operations involving numerical sequences containing multiple quantity cues, but not size-based sequences, already at 4 months of age. Infants were tested in an ordinal task in which they detected and represented increasing or decreasing variations in physical and/or numerical size, and then responded to ordinal sequences that exhibited greater or lesser sizes/numerosities, thus following or violating the OM generated during habituation. Results showed that OM was absent during size ordering (Experiment 1), but was present when infants ordered arrays of discrete elements varying on numerical and non-numerical dimensions, if both number and continuous magnitudes were available cues to discriminate between with-OM and against-OM sequences during test trials (Experiments 2 vs. 3). The presence of momentum for ordering number only when provided with multiple cues of magnitude changes suggests that OM is a complex phenomenon that blends multiple representations of magnitude early in infancy.

Number is a basic property of the environment to which human and non-human animals are spontaneously attuned (Dehaene, 1997;Gallistel & Gelman, 1992).Developmental research has shown that preverbal infants extract numerical information from the environment and represent such information in an abstract form, which holds across sensory modalities (Coubart, Streri, de Hevia, & Izard, 2015;Feigenson, Dehaene, & Spelke, 2004;Jordan & Brannon, 2006;Turati, Gava, Valenza, & Ghirardi, 2013).For instance, newborn infants who hear a sequence of sounds look longer to a visual image containing the same numerosity than to a visual image with a different numerosity (differing by a 1:3 ratio) (Izard, Sann, Spelke, & Streri, 2009).Infants not only detect and represent numerical information, but also operate on such representations to perform numerical transformations.For instance, they perform simple computations, such as addition, subtraction, and ordering.McCrink and Wynn (2004) showed that 9-month-olds look longer to an outcome of 5 than to an outcome of 10 Journal of Numerical Cognition jnc.psychopen.eu| 2363-8761 after familiarization to computerized displays of a 5 + 5 addition event, and longer to an outcome of 10 than to an outcome of 5 after familiarization to a 10 -5 subtraction event.Picozzi and colleagues (Picozzi, de Hevia, Girelli, & Macchi Cassia, 2010) found that 7-month-old infants discriminate changes in the ordinal direction of numerical relations, and do so in the absence of corresponding variations in other non-numerical quantities such as surface area, density, and contour length.After habituation to sequences of three displays whose numerical values increased or decreased by a 1:2 ratio, infants looked longer at subsequent numerical sequences of a reversed ordinal direction; for example, infants who viewed increasing sequences of 6, 12, and then 24 objects during habituation looked longer to a decreasing sequence of 16, 8, and then 4 objects at test.
In adult numerical cognition, it is widely accepted that numerical representations take the form of a 'mental number line'.This model posits that numerosities are spatially represented along a continuum, such that (in Western cultures) small numbers are associated to the left side and large numbers to the right side of space, first evidenced by the so-called SNARC (Spatial-Numerical Association of Response Codes) effect (Dehaene, Bossini, & Giraux, 1993).As the cultural direction of writing and reading exerts an influence on the specific orientation, it has been argued that numerical-spatial associations derive from overlearned scanning habits acquired mainly through reading and writing experience well into the schooled childhood years (Berch, Foley, Hill, & Ryan, 1999;Göbel, Shaki, & Fischer, 2011).However, the last few years have overturned this view, as recent research has shown that infants in their first year of life exhibit a variety of spatial-numerical associations.By 8 months, infants establish a correspondence between number and spatial extent ('more numerous is mapped onto more extent ', de Hevia & Spelke, 2010;Lourenco & Longo, 2010), and associate different numerosities to different lateralized spatial positions (Bulf, de Hevia, & Macchi Cassia, 2016).In particular, Bulf and colleagues (Bulf et al., 2016) found that 8-month-old infants orient faster towards a left-sided cue when previously primed by a central small numerosity, and they orient faster to a right-sided cue when previously primed by a central large numerosity.This evidence suggests that numerical representations have an inherent spatial component, which points to the existence of a spatially oriented numerical representation that is functional in the first year of life.
A recent subfield that helps to unravel the developmental origins of the spatial-numerical associations is the Operational Momentum (OM) effect in arithmetic.The OM effect arises when participants systematically overestimate the outcomes of addition problems and underestimate those of subtraction problems (Knops, Viarouge, & Dehaene, 2009;McCrink, Dehaene, & Dehaene-Lambertz, 2007).This phenomenon has been documented in infancy; when infants are shown videos of addition or subtraction events, and are then presented with three different types of outcomes -one correct, one too large, and one too small-, they look longer to the too small when tested with addition and to the too large when tested with subtraction (McCrink & Wynn, 2009).Overall, OM effects in adults, children and infants have been interpreted by borrowing the original account given in the interpretation of the representational momentum (Freyd & Finke, 1984), in which the anticipated final location of a moving target is displaced forward in the direction of target motion (see review in Hubbard, 2014).Therefore, the OM in arithmetic has been interpreted as arising from the displacement of the anticipated outcome along the spatial numerical representation onto which the numerical transformation is mapped: Toward the left (smaller) for subtraction and toward the right (larger) for addition (McCrink et al., 2007).
Recently, the OM effect has been extended to ordering operations, as it arises even when 12-month-old infants represent increasing/decreasing relations among continuous magnitudes (i.e., size of a single object).In particular, when infants are habituated to an object that progressively increases or decreases in size, and are subsequently presented at test with ordinal sequences that exhibit greater or lesser size, they look longer to size changes whose direction violate the operational momentum experienced during habituation (i.e., the smaller sequence in the increasing condition and the larger sequence in the decreasing condition) (Macchi Cassia, McCrink, de Hevia, Gariboldi, & Bulf, 2016).This evidence indicates that not only numerical information, but also non-numerical quantities -such as size -might be represented as well along a spatially oriented representational continuum in the first year of life.
These findings are at odds with earlier evidence suggesting that the dimension of size does not lead to SNARC-like effects.In fact, Bulf et al. (2016) found that, unlike non-symbolic numerical cues, size cues are not capable to orient spatial attention towards peripheral regions of space in 8-month-old infants.In discussing the discrepancy between the presence of OM for the dimension of size in 12-month-olds and the absence of a size cueing effect in 8-month-olds, Macchi Cassia and colleagues (2016) argued that the phenomenon of mentally spatialize information may emerge first for numerical information and later be extended, possibly by analogy, to other dimensions, such as size.A more intriguing possibility raised by the authors is that the explicit processing of ordinal information, which was present in the Macchi Cassia et al.'s (2016) OM task with 12-month-olds, but absent in the Bulf et al.'s (2016) cueing paradigm with 8-month-olds, might have boosted infants' reliance on spatial codes to represent quantity information.Indeed, there is mounting evidence that, in adults, the coding of serially ordered information co-opts a spatially organized mental representation, as adults exploit a spatially oriented horizontal continuum to represent not only information learnt in a conventional fixed order, like numbers (e.g., Dehaene et al., 1993) or letters of the alphabet (e.g., Gevers, Reynvoet, & Fias, 2003), but also non-ordered newly-learnt information, such as lists of unrelated words (e.g., Previtali, de Hevia, & Girelli, 2010).This evidence has been recently extended to preverbal infants, who, at 7 months, can extract and learn rule-like patterns (i.e., ABB or ABA) specified by items' order in spatio-temporal visual sequences presented along a left-to-right orientation, but not along a right-to-left orientation (Bulf, de Hevia, Gariboldi, & Macchi Cassia, 2017).This finding extends earlier demonstrations that 7-month-olds can extract and learn a numerical ordinal (increasing vs. decreasing) rule when sequences of numerical displays are presented from left to right, but not when presented from right to left (de Hevia, Girelli, Addabbo, & Macchi Cassia, 2014), and 8-month-olds relate an increase in number to an increase in spatial extent (de Hevia & Spelke, 2010).Together, these findings show that space is involved in order processing from the earliest stages of development, when infants lack symbolic knowledge and formal education, and that, at least from the age of 7 months, infants are prone to represent ordered information along a left-to-right spatial continuum.
In light of this evidence, in the present study we exploited the OM effect to investigate the mapping of order into space in infants younger than 7 months -i.e., 4-month-olds -, when exposure to culturally-shaped routines is even more limited.We chose to test infants at this particular age because recent research has shown that 4month-olds are able to extract ordinal information from both numerical and size-based sequences, at least when confronted with increasing order.After habituation to increasing sequences composed of a single shape varying in size by a 1:2 ratio, 4-month-old infants looked longer to a newly-sized sequence of a reversed ordinal direction (Macchi Cassia, Picozzi, Girelli, & de Hevia, 2012).More recently, these findings were extended to numerical sequences of large numerosities that increased/decreased following a 1:3 ratio: Again, infants habituated to increasing numerical sequences looked longer to the reverse order at test (de Hevia et al., 2017).

Operational Momentum for Size and Number Ordering
Because at 4 months infants are able to perform ordering operations on both numerical and continuous magnitudes, by testing for the presence of the OM effect for number and/or size we were able to explore whether the mapping of ordinal information into directional space constitutes an early predisposition that applies to both discrete and continuous magnitudes, or whether it emerges first for number and is later extended to size.
Building on previous research (Macchi Cassia et al. 2012;de Hevia et al., 2017), we tested infants' proneness to show an OM effect by using the ratios that allowed successful ordinal discrimination at 4 months: a 1:2 ratio for size sequences and a 1:3 ratio for numerical sequences.

Experiment 1
In Experiment 1 4-month-old infants were habituated with a series of increasing or decreasing size-based sequences and were then tested with new sequences in which the same ordinal direction was composed of larger and smaller sizes.If infants show an OM effect while ordering size, as they do at 12 months (Macchi Cassia et al., 2016), they should look longer at test to the series that violate the momentum created during habituation: Infants habituated to a series of increasing size should look longer to a series containing smaller sizes at test, and those habituated to a series of decreasing size should look longer to a series containing larger sizes at test.

Methods
Methods were modelled after Macchi Cassia et al. (2016).Specifically, we used the same Stimuli and Procedure as in that earlier study, and accordingly repeat the relevant textual descriptions to describe methods as appropriate.

Participants
Participants were 40 4-month-old infants (22 females, mean age = 4 months 21 days, range = 4 months 3 days to 5 months 0 days) assigned randomly and in equal number (N = 20) either to the increasing or the decreasing order condition.Data from an additional 19 infants were discarded due to fussiness resulting in failure to complete all testing trials (n = 10), looking time in at least one test trial shorter than 1.5 s (n = 7), technical error (n = 1), or parental interference (n = 1).Infants were recruited via a written invitation that was sent to parents based on birth records provided by neighbouring cities.The protocol was carried out in accordance with the ethical standards of the Declaration of Helsinki (BMJ 1991;302: 1194), and approved by the Ethics Committee of the University of Milano-Bicocca.Parents gave their written informed consent before testing began.

Stimuli
Stimuli were single colored shapes varying in area by a 1:2 ratio (range 5.5-84 cm 2 ) and were presented on a white background in the center of the computer monitor.There were five sets of stimuli: Three for the habituation phase and two for the test phase, each set being composed of a different shape displaying a unique color.The three habituation sets contained blue circles, green triangles, and red squares that were, respectively, 9, 18, 36; 11, 22, 44; and 13, 26, 52 cm 2 .The two test sets contained three rainbow-colored bars that expanded/contracted along the horizontal axis and whose sizes were different in each set, with an overall area of 5.5, 11, 22 cm 2 in the smaller set, and 21, 42, 84 cm 2 in the larger set (see Figure 1).The average shape size of the smaller and larger test set differed from the average habituation set by a 1:2 ratio.Bars were used at test to preclude any approaching (looming) or retracting (zooming) percepts (after Macchi Cassia et al., 2012), and rainbow-color was used to increase stimulus saliency (after Brannon, 2002).
Figure 1.The five sets of colored shapes as they were presented to infants in the increasing order condition of Experiment 1. Arrows represent passage of time; objects were presented serially, centered on the screen.Blue circles, green triangles, and red diamonds were presented in a fixed order during habituation, and the smaller and larger sets of rainbow-colored bars were presented, respectively, during the against-OM and the with-OM test trials, with presentation order counterbalanced across participants.For infants in the decreasing order condition the same habituation shapes were presented in reversed order (from the larger to the smaller), starting from the red diamonds and proceeding to the green triangles and the blue circles, and the smaller and larger sets of bars were presented, respectively, during the with-OM and the against-OM test trials.

Design
Infants were habituated to increasing or decreasing sequences of blue circles, red squares, and green triangles, and were then tested with increasing or decreasing sequences containing newly-sized bars (see Figure 1).Half of the infants were randomly assigned to the increasing habituation condition (N = 20).Within each habituation condition, the three different stimulus sets were cycled in a fixed order until infants met the habituation criterion: From the smallest to the largest shape for the increasing condition (i.e., 9-18-36, 11-22-44, 13-26-52 cm 2 ), from the largest to the smallest shape for the decreasing condition (i.e., 52-26-13, 44-22-11, 36-18-9 cm 2 ).The use of a consistent fixed order of presentation of the sets across trials for each of the two habituation conditions provided infants with redundant cues to ordinality between, as well as within, trials (see Macchi Cassia et al., 2012).Following habituation, all infants were given two test trials alternating the withmomentum and the against-momentum sequences of rainbow-colored bars (i.e., 5.5-11-22 and 21-42-84 cm 2 ), with the order of presentation counterbalanced across participants.For infants in the increasing habituation condition the with-momentum test sequence comprised bars measuring 21, 42, 84 cm 2 , and the againstmomentum test sequence comprised bars measuring 5.5, 11, 22 cm 2 ; the opposite was true for infants in the decreasing habituation condition.For both conditions, both test trials exhibited an order (ascension, or descension) that was identical to that displayed in habituation.

Apparatus
Each infant was tested while sitting in an infant seat approximately 60 cm from the monitor where the stimuli were presented (24" screen size, 1920 X 1200 pixel resolution, refresh rate of 60 Hz) in a dimly lit room.A video camera was positioned just above the stimulus presentation monitor and was directed to the infant's face.
The live image of the infant's face was displayed on a television monitor to allow the online coding of the infant's looking times through the E-Prime 1.0 program by the experimenter, who was blind to the habituation condition to which the infant was assigned and to the order of test trials.The image of the infant's face was also recorded via a Mini-DV digital recorder, and for half of the infants in the sample (N = 20) data were subsequently coded offline.Intercoder agreement (Pearson correlation) between the two observers who coded the data live or from digital recording, as computed on total fixation times on each of the two test trials, was r = .997.

Procedure
A cartoon animated image associated with varying sounds served as an attention catcher before the trial began.When the infant looked at the animated fixation point, the experimenter started the trial.Each trial consisted of a repeating cycle (6500 ms in total) that began with a black screen (500 ms) followed by the three shapes.Each shape appeared for 1750 ms on a white background, and was preceded by a 250 ms white interstimulus interval (ISI) to reduce the impact of looming/zooming cues.Each trial continued until the infant looked continuously for a minimum of 500 ms and ended when the infant looked away continuously for 2 s or looked for a maximum of 60 s.The three habituation stimulus sets were presented in a fixed order and repeated until the infant saw a maximum of 12 trials or met the habituation criterion, which was defined as a 50% decline in looking time on three consecutive trials, relative to the looking time on the first three trials.Following the habituation phase, infants were given two test trials, a with-momentum sequence and an against-momentum sequence, with half of the infants seeing the with-momentum sequence first.

Results and Discussion
All statistics are two-tailed.The average number of trials received during habituation did not differ for infants tested in the the increasing and decreasing order conditions (M = 7.45, SEM = 0.43 vs. M = 8.7, SEM = 0.62), t(38) = 1.67, p = .1).However, infants in the decreasing order condition needed more time overall to habituate than infants in the increasing condition (M = 70.83s, SEM = 10.39 vs. M = 44.28s, SEM = 6.97, t(38) = 2.12, p = .04),suggesting that information processing for the abstraction and representation of increasing order is less effortful than for decreasing order.A similar variation in habituation looking times did not emerge when considering only the first three and the last three habituation trials.A two-way analysis of variance (ANOVA) on mean habituation looking times with order condition (increasing vs. decreasing) as the between-participants factor and habituation trials (first three vs. last three) as the within-participants factor confirmed the presence of a significant overall decrease from the first three (M = 10.82 s, SEM = 1.2) to the last three habituation trials (M = 4.75 s, SEM = 0.5), F(1,38) = 35.18,MSe = 736.72,p < .001,η 2 p = .48,in the absence of a main effect or interaction involving the factor order condition (ps > .26)(see Figure 2).To determine whether during test trials infants looked longer to the ordered sequence that violated the momentum effect, as generated by the abstraction of the ordinal rule during habituation, mean looking times to the two test trials were entered into a three-way ANOVA with order condition (increasing vs. decreasing) and test order (with-OM first vs.against-OM first) as between-participants factors and test trial type (with-OM vs. against-OM) as within-participants factor.The analysis revealed no significant main effects or interactions (all Fs < 1.65, ps > .2),indicating that looking times to the against-OM test trial did not differ from those to the with-OM trial for infants in either the increasing (M = 5.74 s, SEM = 0.9 vs. M = 6.1 s, SEM = 0.93) or the decreasing (M = 7.7 s, SEM = 1.04 vs. M = 7.4 s, SEM = 1.14) order conditions (see Figure 2).Finally, binomial tests confirmed the absence of an OM effect in this experiment, revealing that 22 out of 40 infants looked longer to the against-OM test trial compared to the with-OM one (22 vs. 18, p = .6;two-tailed), with a similar number of infants showing the pattern in the increasing and decreasing conditions (9 vs. 13, n.s.).
Overall, results show that infants did not manifest a differential looking behavior toward test sequences whose elements' size violated the momentum effect, relative to those whose elements' size followed the momentum.This pattern suggests that, unlike older, 12-month-old, infants (Macchi Cassia et al., 2016), 4-month-olds did not experience a momentum effect while ordering size.This may indicate that ordering operations do not elicit OM effects early in development (i.e., by 4 months of age); another possibility is that OM effects are absent in earlier stages of development for the dimension of size, but might be present for the dimension of number.This possibility builds on previous demonstration that the link between magnitude and space, as evident in spatial attentional tasks, is specific to number at 8 months and does not extend to the dimension of size (Bulf et al., 2016).

Experiment 2
In Experiment 2, a new group of 4-month-old infants was habituated to a series of either increasing or decreasing numerical sequences and then tested with new sequences in which the same ordinal direction was composed of larger or smaller numerosities.If infants experience an OM effect while ordering number, then they should look longer at the test series that violate the momentum created during habituation: Those habituated to increasing number should look longer to smaller test numerosities, and those habituated to decreasing number should look longer to larger test numerosities.Numerical sequences included numerosities that varied by a 1:3 ratio, as infants at this age succeed in numerical ordinal tasks when provided with this ratio (de Hevia et al., 2017).

Methods
The methods were the same as in Experiment 1, except as follows.

Participants
The final sample included 40 4-month-olds (20 females, mean age = 4 months 17 days, range = 3 months 28 days to 5 months 4 days) assigned randomly and in equal number (N = 20) either to the increasing or the decreasing order condition.Data from an additional 19 infants were discarded due to fussiness resulting in failure to complete all testing trials (n = 6), looking time in at least one test trial shorter than 1.5 s (n = 12), or technical error (n = 1).Parents gave their written informed consent before testing began.

Stimuli
The five stimulus sets used in the current experiment were created after de Hevia et al. (2017), in which 4month-olds showed successful discrimination of numerical order.They were generated using E-Prime 1.0 software, and consisted of five sequences of three numerical arrays each containing colored rectangularshaped items enclosed in a white area, randomly arranged, with the item's shorter side aligned with the horizontal plane.Three different exemplars were generated for each stimulus set that differed in item configuration.Three of the five sets were used for the habituation phase, and two for the test phase.The habituation sets were composed of 8-24-72, 9-27-81, and 10-30-60 blue (rgb: 0, 0, 255) items, and the two test sets were composed of 5-15-45 and 16-48-144 purple (rgb: 201, 28, 195) items.The shape of the white envelope area enclosing the items varied across the habituation sets and was the same within each set, although its size was positively correlated with numerosity (i.e., smaller numbers were enclosed in smallersized envelope areas and larger numbers in larger-sized areas) (see Figure 3).Therefore, density was constant across numerosities in each given habituation set, while envelope area and cumulative surface area were positively correlated with number.In fact, item size was constant at 0.18 cm 2 , and density was 0.06 elements per cm 2 for all numerosities.Inversely, in the test sets, both the shape (i.e., hexagon) and the size of the envelope area were constant across numerosities so that density covaried with number, and non-numerical continuous variables were controlled both within and between sets by keeping cumulative surface area constant.In fact, item size was inversely correlated to number: The size of each single item in the smaller, medium and larger numerosity displays was, respectively, 0.45 cm 2 , 0.15 cm 2 and 0.05 cm 2 in the 16-48-144 test set, and 1.44 cm 2 , 0.48 cm 2 and 0.16 cm 2 in the 5-15-45 test set, and cumulative surface area was constant at about 7 cm 2 .Overall, non-numerical variables that varied during habituation were held constant during test, and vice-versa.
Figure 3. A) The five sets of numerical displays as they were presented to infants in the increasing order condition of Experiment 2. Arrows represent passage of time; objects were presented serially, centered on the screen.The numerical sequences 8-24-72, 9-27-81 and 10-30-90 were presented in a fixed order during habituation, and the numerical sequences 5-15-45 and 16-48-144 were presented, respectively, during the against-OM and the with-OM test trials, with presentation order counterbalanced across participants.For infants in the decreasing order condition, the same habituation displays were presented in reversed order (from the larger to the smaller), starting from the 90-30-10 sequence and proceeding to the 81-27-9 and the 72-24-8 sequence, while the 45-15-5 and the 144-48-16 sequences were presented, respectively, during the with-OM and the against-OM test trials.B) The five sets of numerical displays as they were presented to infants in the increasing order condition of Experiment 3. Habituation sets were identical to those used in Experiment 2, whereas the two test sets included the same number of items as in Experiment 2 (5-15-45 and 16-48-144) but differed for cumulative surface area (8 cm 2 and 26 cm 2 , respectively).
s, SEM = 0.85; decreasing condition: M = 6.8 s, SEM = 1.6 vs. M = 4.9 s, SEM = 0.6) (see Figure 4).Binomial tests confirmed that only 15 out of 40 infants looked longer to the against-OM test trial compared to the with-OM one (15 vs. 25, p = .8,two-tailed), with a similar number of infants showing the pattern in the increasing and decreasing order condition (8 vs. 7, n.s.).Results show that infants fail to exhibit an OM effect while ordering numerical sequences, as indexed by their comparable looking times at both ordered test sequences, the one violating the OM and the one following the OM generated during habituation.When considered together with the results of Experiment 1, this finding suggests that at 4 months of age ordering of both discrete and continuous quantities do not engender momentum-like effects.When the two test sequences differed only by numerical information, as non-numerical variables were strictly controlled, no OM effect was observed.
Research on infant numerical cognition has consistently shown that providing infants with multiple cues boosts their sensitivity to numerical differences (Jordan, Suanda, & Brannon, 2008) as well as their ability to extract ordinal numerical relations (Suanda, Tompson, & Brannon, 2008).Therefore, in Experiment 3 we tested a new group of 4-month-old infants using a new set of test stimuli, in which the magnitude difference between the with -OM and the against-OM sequences was provided not only by number, but also by cumulative surface area, as the two cues covaried one with the other between the sequences (the habituation stimuli for Experiment 3 remained identical to those in Experiment 2).In so doing, we increased the saliency of the magnitude variation that might allow infants to differentiate the two test trials, and therefore reveal the momentum generated during habituation.

Experiment 3
In Experiment 3, a new group of 4-month-old infants was habituated with a series of either increasing or decreasing numerical sequences and then tested with new sequences in which the same ordinal direction was composed of larger and smaller numerosities.During test, however, they received multiple cues to magnitude differences between test trials, as not only number differed across trials, but also cumulative surface area.
Unlike in Experiment 2, this dimension covaried with number across the with-OM and the against-OM test sequences.Again, if infants experience an OM effect while ordering number, then they should look longer at the test series that violate the momentum created during habituation: Those habituated to increasing number should look longer to smaller numerosities, and those habituated to decreasing number should look longer to larger numerosities.In Experiment 3, as in Experiment 2, numerical sequences included numerosities that varied by a 1:3 ratio.

Figure 2 .
Figure 2. Overall mean total looking time (±SEM) to the first three and last three habituation trials, and to the with-OM and against-OM test trials displayed by infants in the increasing and decreasing order conditions in Experiment 1. Infants failed to show discrimination between the with-OM sequence and the against-OM sequence.

Figure 4 .
Figure 4. Overall mean total looking time (±SEM) to the first three and last three habituation trials, and to the with-OM and against-OM test trials displayed by infants in the increasing and decreasing order conditions of Experiment 2. Infants failed to show discrimination between the with-OM sequence and the against-OM sequence.