Is Finger Digit Ratio Seen in a Baby

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Open Access

Peer-reviewed

Research Article

Digit Ratio Predicts Sense of Direction in Women

• Xiaoqian J. Chai,
• Lucia F. Jacobs

x

• Published: February 29, 2012
• https://doi.org/10.1371/periodical.pone.0032816

Figures

Abstract

The relative length of the second-to-fourth digits (2D:4D) has been linked with prenatal androgen in humans. The 2D:4D is sexually dimorphic, with lower values in males than females, and appears to correlate with various measures of behavior. However, the relationship betwixt digit ratio and cognition, and spatial noesis in particular, has produced mixed results. In the nowadays written report, we hypothesized that spatial tasks separating cue conditions that either favored female person or male person strategies would examine this construction-office correlation with greater precision. Previous work suggests that males are meliorate in the utilise of directional cues than females. In the present report, participants learned a target location in a virtual landscape surroundings, in atmospheric condition that contained either all directional (i.eastward., distant or compass bearing) cues, or all positional (i.east., local, small objects) cues. Later on a brusk delay, participants navigated dorsum to the target location from a novel starting location. Males had higher accuracy in initial search direction than females in environments with all directional cues. Lower digit ratio was correlated with higher accuracy of initial search direction in females in environments with all directional cues. Mental rotation scores did not correlate with digit ratio in either males or females. These results demonstrate for the beginning time that a sex difference in the use of directional cues, i.e., the sense of direction, is associated with more male-like digit ratio.

Citation: Chai XJ, Jacobs LF (2012) Digit Ratio Predicts Sense of Direction in Women. PLoS 1 seven(2): e32816. https://doi.org/10.1371/journal.pone.0032816

Editor: Andrew Whitehouse, The University of Western Australia, Australia

Received: June 8, 2011; Accepted: February half dozen, 2012; Published: February 29, 2012

Copyright: © 2012 Chai, Jacobs. This is an open up-access commodity distributed nether the terms of the Creative Eatables Attribution License, which permits unrestricted utilize, distribution, and reproduction in whatsoever medium, provided the original author and source are credited.

Funding: This inquiry was supported by NSF ECCS-1028319, an NSF Graduate Student Fellowship to X.J. Chai and the Rennie Epilepsy Fund grant to Fifty.F. Jacobs. The funders had no role in study blueprint, data collection and assay, decision to publish, or preparation of the manuscript.

Competing interests: The authors take declared that no competing interests be.

Introduction

The ratio of the second to the fourth finger length on the right paw (2D:4D, or digit ratio) is putatively a marker of the organizational effect of prenatal testosterone in humans ([1], see [two], [3], [4], [5] but run across [6], [7]). It is sexually dimorphic, with women having higher ratios than men on average [8], [nine], [10]. It has been hypothesized that 2D:4D reflects prenatal androgen levels and the individual's sensitivity to androgens [2]. There is indirect evidence that supports such hypothesis in humans. Higher (more feminized) second:4D ratios were reported in females with androgen insensitivity syndrome [6]. Individuals with congenital adrenal hyperplasia (CAH), a status associated with loftier levels of prenatal androgens, have been found to take smaller 2d:4D ratio [11], [12], [xiii], [xiv]. Sexual dimorphism in digit ratio has also been found in a number of non-human species, including rodents [xv] and anthropoid primates [sixteen]. A study that directly manipulated hormone level in significant rats showed that elevated level of maternal testosterone resulted in lower 2D:4D ratios in offsprings [17]. The relative level of prenatal testosterone and oestrogen signaling during a narrow window of fetal evolution has been recently shown to accept a causal effect on 2d:4D in mice ([xviii], see [19]).

Many spatial abilities are sexually dimorphic and appear to be influenced by prenatal testosterone [20]. Therefore 1 might wait digit ratio to correlate with spatial ability. However, previous research on the relationship between spatial ability and digit ratio has produced mixed results [21], [22], [23], [24]. Some found no meaning correlations between digit ratio and spatial ability [10], [25], [26], others have reported both negative [23], [24] and positive correlations [10] in males or females. A recent meta-analysis past Puts, et al. (2008) [27] analyzed the effect size (correlation coefficients between 2D:4D and spatial power), and found the effect size across studies to be negligible, for either males or females. However, the majority of the studies published so far, including the ones reviewed by Puts et al. (2008) assessed spatial ability using only two-dimensional tasks, such every bit the mental rotation examination (MRT). Yet information technology is unclear how such tasks relate to operation in spatial navigation [28]. To our noesis, only ii studies take examined the human relationship of digit ratio and navigation with a three-dimensional (3D) spatial task. Both studies used a maze-learning job adapted from the rodent Morris water maze [26], [29]. Neither study found the expected relationship between digit ratio and spatial abilities. The Morris water maze requires participants to navigate to a hidden platform within the exam arena using external distal cues. Males typically need less fourth dimension (latency to target) before learning the target location in virtual simulations of this blazon of maze [28], [thirty]. Because of the robust sexual practice difference in Morris water maze, which favors males, one might expect a lower digit ratio (i.due east., more than masculine) to be associated with shorter latencies. Yet Csatho et al. (2003) [29] reported that lower digit ratio (i.e., more masculine) was associated with a longer search latency in females. The authors too reported that lower digit ratio was associated with ameliorate post-test navigational cue identification. This result was as well non expected since females oft outperform males in object location call up [31], [32], [33], [34]. A higher ratio (more feminine) might be expected to correlate with better cue identification. This important study has therefore raised many open questions.

A possible reason for this conflicting finding on the human relationship between digit ratio and navigation abilities in the Csatho et al. (2003) study is the nature of the tasks being used. Spatial navigation almost likely recruits multiple cognitive abilities, and the recruitment of the specific power may vary between the sexes, with females and males relying on different sets of cues to orient. In rodents, females are notably sensitive to the unique features of discrete objects whereas males are sensitive to extra-maze cues such every bit the geometry of the enclosure [35], [36], [37], [38], [39], [40]. Similar results accept been shown in humans [41], [42]. Males relied more on geometric information than females [41], whereas females are frequently more sensitive to the switching of local object location [31], [43]. This raises the possibility that the human relationship between digit ratio and navigation operation is particularly sensitive to the types of cues that are bachelor in the environment. For example, cues that are preferentially used by males, such as distant cues and geometrical shape of the space, should be more closely correlated with lower digit ratio.

In the parallel map model of the cerebral map [44], the map is created by integrating data from ii distinct functional cue classes: directional and positional cues. Directional cues provide primarily directional (compass) information. Distal landmarks, for example, are as well far away to provide authentic positional information but can nevertheless give a directional begetting. Similarly, extended cues such as gradients (smell, light or terrain slant), or geometric cues primarily provide directional information. In contrast, positional cues are discrete and local objects, which provide relatively precise positional information inside a local cue assortment. The model predicts a male person advantage in environments that are rich in directional cues and female advantage in environments that are rich in positional cues. Evidence supporting this prediction was reported from tasks involving manipulations of directional and positional cues in the stimuli [42], [45].

Given the possibility that the functional class (whether primarily directional or positional) of cues in a spatial surroundings might impact the performance of males and females in different ways, one interpretation of the dissonant results in the Csatho et al. (2003) [29] study, is that the physical layout of the task could have prevented the use of the male-preferred directional cues. The maze used in the Csatho et al. (2003) report was a circular arena containing intra-maze object cues (i.e., positional cues). This would have biased spatial learning to what would usually exist a female-similar strategy. The apply of a male-like strategy, which depends on the distant cues outside the maze, would have been prevented past the tall non-transparent walls surrounding the maze. Therefore, under these chore weather, any furnishings of the digit ratio that was correlated with to male spatial strategy would have been muted or reversed.

In the present study, nosotros examined the relationship between digit ratio and spatial navigation ability by decision-making the exact nature of navigation cues in a virtual environment. Nosotros propose that a lower digit ratio (more masculine) should be associated with male person-like spatial strategies and hence predict superior functioning in the presence of directional, but not positional, cues. Nosotros hypothesized that the 'sense of direction' in spatial navigation is near sensitive to directional cues. We therefore examined the relationship between digit ratio and navigation orientation accuracy in a virtual navigation study with controlled cue types in the surround, containing either all directional cues or all positional cues. In addition, we too measured mental rotation test scores to determine if digit ratio relates to spatial visualization tasks such equally the MRT the same way every bit 3D virtual navigation. Because sexual activity differences in MRT are and so well established, we likewise used the MRT to confirm that a typical cerebral sexual activity difference pattern (i.e., male reward) could be demonstrated in our sample.

Materials and Methods

Ideals Statement

All protocols were canonical by the Academy of California at Berkeley's Commission for the Protection of Human Subjects. All participants gave informed written consent prior to the experiment.

Participants

Eighty-two undergraduate students (41 females, ages 19.8±ane.9; 41 males, ages 19.2±ane.ane) participated in the virtual navigation task, completed the mental rotation test and had their finger lengths measured. Mental rotation exam scores were missing in four males due to figurer error. Due to a technical mistake with the flatbed scanner, the incorrect size of the hand images was saved for a subset of subjects. Equally a result, three females and 11 males did not have measurements of their absolute finger lengths. The accuracy of the 2D:4D ratio of these subjects, however, was not afflicted past the scanner image size. Therefore we included second:4D data from all 82 subjects in our analysis. Navigation accuracy information (distance from the hidden target at the finish of probe trial) in these participants was previously described in Chai and Jacobs (2009) [46]. Data presented here have not been reported elsewhere.

Apparatus

We constructed computerized 3-dimensional virtual environments (VE) using a commercially bachelor video game engine (Unreal Engine two by Epic Games, Raleigh, NC). These environments were presented on a 21-inch computer monitor with participants sitting approximately 55 cm in front end of the monitor. Horizontal field of view was approximately 39 degrees and vertical field of view was approximately thirty degrees. Participants used a joystick (Cyborg Evo by Saitek, Bristol, Britain) with forwards, backward, left-turn and correct-turn options to motion in the environment. Coordinates of the move were recorded into a log file every 0.2 s.

Virtual environments (VE)

The VE task was modeled later the logic of the Morris water maze chore, in which the participant must locate a unmarried hidden target in a circular arena. Equally shown in Figure 1, the VE was a large grassy terrain that contained a test arena surrounded by an octagonal invisible debate that was 18.3 virtual meters in radius. The fence was invisible to ensure an unblocked view of the surrounding cues. The target was a blueish spike-like crystal. Two types of environments were synthetic, one for the all-directional-cue condition and one for the all-positional-cue condition. In the all-directional-cue environs, the exam arena was located on a pocket-size colina with a terrain slant of approximately 30 degrees. Other directional cues included a river running at the bottom of the slope, the sun, and a deject-filled sky (Figure 1A–B). In the all-positional-cue environments, the test arena was situated on a apartment terrain with objects such as rocks, small plants, wooden barrels and mushrooms forming object clusters of unlike configurations within the arena. The target was located in i of the clusters. Because duplicates of the same objects were found at different locations, the job could non be solved by simply associating the target location with a unmarried object (Figure 1C–D).

Figure i. Representative virtual environments for the different cue course trials.

Screenshot of a directional-cue trial (A), screenshot of a positional-cue trial (B), schematic of the directional-cue surround (C) (the arrow points up the slope), schematic of a positional-cue environs (D). The blue crystal (target) was located in one of the cue clusters.

https://doi.org/10.1371/periodical.pone.0032816.g001

Procedure

Virtual navigation task.

Prior to starting the navigation trials, participants were given a brusk exercise session to familiarize themselves with the VE interface and to do moving with the joystick. All participants reported they were comfortable with moving in the VE at the cease of the practice trials.

Navigation trials commenced immediately after practise trials. There were half-dozen trials for each of the ii conditions (directional cue and positional cue). The trials were presented in pseudo-random social club. Each trial consisted of two phases: a training phase and a probe phase, each 25 s in duration. In the training phase, the target was visible throughout the trial. Participants were told to explore the area and endeavour to memorize the location of the target. Each training stage was followed immediately past the probe phase, in which the target was hidden. Participants had twenty s to arroyo as closely as possible to the target location in the probe phase. The starting point of the participant was unlike in the training stage and the probe phase. A timer was displayed on the meridian left corner of the screen to help participants keep track of time. At the end of the 20 s, the target re-appeared for 5 s to give participants feedback on their operation. If the participant finished the search before 20 s, they were told to remain at their last search location and wait for the feedback at the finish of the trial. There was a 10 s inter-trial fixation on a centered cross on the monitor. The location of the target was unlike in each of the six trials for both directional-cue and positional-cue trials. Each positional-cue trial used different object cues and dissimilar object locations.

Orientation ability in virtual navigation was accessed by accuracy in the initial search direction. Heading error, which measures orientation error towards the target, has been used every bit the archetype measure out for orientation accuracy in prior navigation studies [47], [48], [49], [50]. Heading error was defined as follows: the deviation of the heading management at any given point along the path from the optimal direction, ranging from naught (aforementioned every bit the optimal management) to 180 degrees (opposite from the optimal direction), with chance level at 90 degrees. The average initial heading error from each point along the kickoff 200 virtual units traveled was used in the assay. The lower the initial heading mistake, the more accurate the initial orientation.

Mental rotation examination (MRT).

Later on the virtual navigation task, participants completed the mental rotation exam. Nosotros used the Peters redrawn version of the mental rotation test originally constructed by Vandenberg and Kuse (1978) [51]. The object images from the original written examination were scanned into jpeg files and displayed on a reckoner screen. Each problem consisted of 1 original object and four possible choices, two of which were rotated versions of the original image. Participants were given 3 min to pick the rotated images for 24 problems. One betoken was given if both right images were picked equally suggested by Peters (1995). This scoring procedure is dissimilar from the conventional scoring organisation past Vandenberg and Kuse (1978).

Digit ratio measurements.

After the completion of the virtual navigation task and the mental rotation task, digital images of the right hand were obtained for digit length measurements using a flat-bed scanner. Participants were told to place their right paw in the eye of the scanner with their palm facing down and rings removed. The encompass of the scanner was then closed before the image of the hand was obtained. No extra pressure level was applied. The second (index) and 4th (ring) finger lengths were later measured from the images from the bottom crease where the finger meets the palm to the tip of the finger using the computer software ImageJ one.37v [52]. The hand images were measured by i of the authors (X.J.C), and by an contained observer. Inter-rater reliability of the digit ratio equally measured past intra-class correlation was 0.983. The average of digit ratios from the two raters was used in the data analysis.

Results

Digit ratio was lower in males than females (males, .953±.031; females, .970±.035; t₈₀  = 2.45, P = .017; Figure 2A). Males had higher MRT scores than did females (males, 6.59±two.17; females, 4.37±two.41; t₇₆  = 4.27, P<.001; Figure 2B). The effect size (Cohen'southward d) was .51 for the sexual practice difference in 2nd:4D and .97 for the sex difference in MRT. In the virtual navigation job, males had lower mistake in initial heading error (college accuracy in search direction) compared to females in the directional cue status (t₈₀  = three.11, P = .003), but not in the positional cue condition (t₈₀  = 1.40, P = .17) (Figure 3). MRT scores did not correlate with initial heading fault in either positional or directional cue in either males or females (ps>.15).

To assess how digit ratio relates to orientation accurateness in navigation, we conducted an analysis of covariance (ANCOVA) for each cue condition, with heading error as the dependent variable, second:4D, sex activity and the interaction between second:4D and sex every bit independent variables. Within-sex posthoc tests were performed merely when at that place was a pregnant relationship between 2D:4D and the dependent variable. We also conducted the same analysis for MRT scores. Out of these 3 tests, the effect of digit ratio was pregnant for heading error in the directional cue condition (F_1,77  = vii.54; P = .008; P = 0.024 later Bonferroni correction), simply not for heading error in the positional cue status (F_1,77  = one.21; P = .28). The relationship betwixt MRT and digit ratio was not significant (F_1,73  = 0.63; P = .43).

We then conducted posthoc correlation tests within each sexual practice only if the main exam describe above was significant, i.eastward., between digit ratio and with heading error in the directional cue condition. Higher digit ratio was associated with greater mistake in initial heading in females (r = .40, P = .01; Figure 4) simply not in males (r = .17, P = .29). Females with low digit ratio were therefore more accurate in their initial orientation.

Discussion

The relationship between digit ratio, a putative marker of organizational hormone furnishings, and spatial abilities has been controversial. Hither we tested participants in two distinct navigational environments (directional or positional cues only), which allowed u.s. to examine this question with greater precision. Our results demonstrate a link between digit ratio and spatial orientation ability in a virtual landscape. In females, digit ratio predicted initial search direction accuracy, i.e., the 'sense of direction', when but directional cues were bachelor. This suggests that females with lower digit ratio had better orientation abilities under specific conditions that commonly favor males, i.e., when they were required to rely solely on directional cues in the navigational environment. These results are consistent with our hypothesis derived from the parallel map model, which predicts a male person advantage in environments with but directional cues. Since directional cues are ameliorate encoded and used by males [42], [46], a more masculine digit ratio (i.e., lower) should predict ameliorate spatial performance under directional cues. Our results propose that directional-cue based mapping, the near primitive feature of the cognitive map [44], is organized at an early stage in brain evolution. Females with lower 2d:4D (putatively higher prenatal androgen levels) may have developed a masculinized cognitive mapping strategy, relying much more on orientation to directional cues than females with higher digit ratios. Nosotros did not observe evidence for a human relationship betwixt male second:4D and spatial orientation accurateness. 1 interpretation for the lack of second:4D effect in males is that any "above-threshold" prenatal androgen exposure in males was not beneficial for their spatial ability. Our findings are consistent with data from congenital adrenal hyperplasia (CAH), a status with loftier fetal testosterone. CAH males have been shown to have similar or worse spatial performance scores compared to controls, whereas females with CAH showed improve spatial ability than unaffected females, and performed at like levels to unaffected males [20], [27], [53], [54]. CAH females announced to accept masculinized 2D:4D, as well as superior spatial ability. It would exist interesting to study them in separate cue conditions (directional or positional cue), to test if they have male-similar strategy in spatial cue apply. Our results are also in accordance with research in rats, where testosterone handling in neonatal rats improved spatial ability in females merely not in males [55]. Neonatal testosterone treatment in females was thought to induce the development of a male-similar hippocampus [56].

We did non find correlations between digit ratio and orientation accuracy in the positional cue condition. This negative result was not unexpected. Although some studies [57], [58], [59] have replicated the female advantage in object location retentivity originally reported by Silverman and Eals (1992) [31], others have failed to reproduce this effect [32], [42], [lx], [61], [62]. Saucier et al. (2007) suggested the female advantage in object location memory was dependent on whether the objects were close (peri-personal space) or relatively far (extra-personal) from the participant's body [43]. Our previous information suggested that the female advantage in positional cue conditions was less robust than the male advantage in directional cue weather condition [42]. Furthermore, we surveyed spatial strategy preferences in the participants in our previous report [46]. Men reported greater preference on a survey (global) representation, which depends heavily on directional cues, whereas preferences on landmark-centered strategies, which depend on positional cues, did not differ between the genders. This lack of sexual practice differences in positional-cue-centered strategy is reflected in the similar accuracy in initial search directions in males and females nether the positional cue condition. Our results underscore the importance of defining the types of cues in the environment and the nature of the job, prior to measuring hormonal furnishings, whether organizational or activational, on sex-specific spatial abilities. Both the Csatho et al. (2003) [29] and Nowak et al. (2010) [26] studies included positional cues in their environment, which could have masked the effect from directional cues. Therefore it was non surprising that they did not find a relationship between digit ratio and spatial power in the expected direction.

The positional cue condition required greater memory load compared to the directional cue condition. Although this was not optimal, the task was designed this way due to the post-obit reasons: one) our airplane pilot data suggested that performance was much worse in the directional cue condition than the positional cue condition. Keeping the directional cue environment the same beyond the experiment was partly an attempt to match the two weather in level of difficulty; 2) in real life, we typically employ the same set of directional cues throughout the course of navigation, whereas when a navigator moves through a spatial surroundings, they need to update the set of positional cues that guides their navigation.

The mental rotation chore has become the standard spatial visualization chore for studying the effects of digit ratio on spatial noesis. In concordance with the meta-assay by Puts et al. (2008) [25], we did not observe a correlation between mental rotation scores and digit ratio. Our findings suggest that sub-components of spatial ability should be examined separately in hereafter studies. We propose that the literature has relied on a depression resolution definition of spatial ability, conflating behaviors such as spatial orientation with mental rotation. The contribution of the parallel map model is to distinguish finer subcategories of spatial orientation, i.e., directional bearing, which in this model is a trait more accurately encoded and performed by males. Nosotros propose that using finer grained cognitive tests is the way forward to resolving the inconsistent pattern of results in the literature.

Activational effects of adult circulation hormones have been reported to affect spatial ability [62], [63]. Although without directly measuring circulating gonadal hormone levels, we can not completely rule out the culling estimation that female participants with low 2D:4D in our study had lower circulating estrogen or high testosterone, other evidence suggest this is unlikely to be the case. A recent study that included a large data sample (160 women and 177 men) did non find a correlation betwixt salivary testosterone and spatial power [64]. Moreover, a meta-assay by Honekopp et al. (2007) [5] found no association between adult sex hormone and digit ratio. Therefore the correlation between digit ratio and spatial ability observed in the present study is more likely to reflect the system consequence of testosterone on spatial knowledge. Yet, it is important to point out that the mechanism linking digit ratio and sexually dimorphic traits is yet nether contend. Although there is testify that suggests androgen receptor factor may influence digit ratio [six], [65], several studies accept not replicated this finding and suggest other mechanisms may be involved [7], [66], [67]. Neonatal testosterone levels may besides modulate 2D:4D [68]. Activational consequence of testosterone on social cognition has been shown to be dependent on 2nd:4D, peradventure being facilitated by the early organizational effect of testosterone [69]. Futurity studies are needed to elucidate the verbal nature of the relationship between second:4D and the organizational and activational effects of sex activity hormone on cognition.

Acknowledgments

Nosotros give thanks Michael Peters for providing the examination stimuli for the mental rotation task. We thank Jillian Jarret, Ruby Ha, Kevin Liu and Christiane Mietzsch for their technical assistance in collecting information.

Author Contributions

Conceived and designed the experiments: XJC LFJ. Performed the experiments: XJC. Analyzed the data: XJC. Contributed reagents/materials/analysis tools: XJC LFJ. Wrote the newspaper: XJC LFJ.

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Source: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0032816