Sex differences in object location memory: The female advantage of immediate detection of changes
Introduction
Object location memory has been considered to be the only spatial ability for which females display superior performance to that of males (e.g., Eals and Silverman, 1994, McBurney et al., 1997, Silverman et al., 2007, Silverman and Eals, 1992). Silverman et al. (2007) assessed the universality of both male and female spatial aptitude across 40 countries and 7 ethnic groups using a worldwide internet-based study. In their study, participants' spatial abilities were measured using Silverman and Eals' (1992) object location memory test and a shortened version of the Peters et al. (1995) version of Vandenberg and Kuse's (1978) group test of three-dimensional mental rotation. Men in all seven ethnic groups and 40 countries scored significantly higher than women on a test of three-dimensional mental rotation. In contrast, women scored significantly higher than men on a test of object location memory in all seven ethnic groups of residents in 35 of the 40 countries assessed (Silverman et al., 2007). These findings underscore the universal advantage of human females in object location memory. The authors inferred that the observed sex differences in cognitive abilities are the result of sex-specific evolution. Silverman and Eals (1992) proposed one such theory that was intended to explain human sex differences in spatial abilities: the hunter–gatherer theory. According to this theory, spatially related sex differences might be explained more accurately in terms of qualitatively different competencies between the sexes rather than quantitatively different ability levels (Eals and Silverman, 1994, Silverman et al., 2007, Silverman and Eals, 1992). In particular, this theory holds that in evolutionary terms, the critical factor influencing human spatial sex differences was division of labor: males functioned primarily as hunters and females as gatherers of plant foods. Therefore, spatial abilities associated with hunting were selected in males, but object location memory was selected in females because this latter ability is associated with successful food gathering (Eals and Silverman, 1994, Silverman et al., 2007, Silverman and Eals, 1992).
The primary purpose of this study is to examine sex differences in long-term retention of object location. The hunter–gatherer theory holds that successful gathering would have entailed locating edible plants among diverse configurations of vegetation and then finding them again in subsequent growing seasons (Eals and Silverman, 1994, Silverman et al., 2007, Silverman and Eals, 1992). Advantageous attributes for females would therefore include not only the capacity to learn rapidly and remember the contents of object arrays, but also the ability to recall the location of each object for a longer period of time. In terms of our study, if the hunter–gatherer theory were correct, females would perform more successfully than males at long-term retention of data in Silverman and Eals' object location memory task. Although results of some previous studies showed that the female advantage in object location memory is fully or partially replicated (e.g., Eals and Silverman, 1994, James and Kimura, 1997, Silverman et al., 2007, Voyer et al., 2007), few researchers have examined the effects of sex differences on long-term tasks of this kind. For example, De Goede and Postma (2008) investigated the sex differences in memory for objects and their location after a retention interval (average retention interval: 52.7 min), in which four filler tasks were administered to participants. In their study, each participant's object location memory was assessed as the Rooms Task, which was adapted from Caldwell and Masson (2001).The results demonstrated that females can better associate objects with locations or simply retrieve locations, independent of the object identity memory. This finding suggests that a female advantage is apparent on the long-term retention on object location-memory. Nevertheless, no reports of previous studies describe sex differences in long-term retention revealed using Silverman and Eals' object location memory task. Generally, the score of Silverman and Eals' object location memory task sums the number of correct detections of location-exchanged objects and the number of correct recognitions of location-maintained objects. This procedure assumes that participants' recognition scores show no sex differences between correct recognition of location-exchanged and location-maintained objects. Silverman and Eals (1992) claimed a female advantage in object location memory because of better location memory for objects included in a complex array. If so, one would expect Silverman and Eals' object location memory task to reveal female advantages not only in the recognition of location-maintained objects, but also in the identification of location-exchanged objects. However, the findings of several studies raise doubts about this assumption because spatial location memory in both sexes appears to be sensitive to stimulus features and tasks' procedural characteristics (Alexander, 2005, Choi and L'Hirondelle, 2005, Dabbs et al., 1998, Gallagher et al., 2006, James and Kimura, 1997, McDuff and Hampson, 2000, McGivern et al., 1998, Postma et al., 1998). For example, James and Kimura (1997) reported that women outperformed men on Silverman and Eals' location memory task when the locations of two objects were exchanged, but not when objects were shifted to sites that had been previously unoccupied by another object. This finding suggests that the female advantage is limited to detection of location-exchanged objects in this task. However, previous studies did not examine sex differences of those recognition scores using Silverman and Eals' object location memory test. For that reason, in this study, we investigated sex differences in the long-term retention of object location and in the ability to recall both location-exchanged and location-maintained objects on this test.
Section snippets
Participants
This study examined the performance of 84 graduate and undergraduate students at Tohoku University (40 men and 44 women). Their mean ages were 21.54 years.
Materials and procedure
We used James and Kimura's (1997) modified version (Location-Exchange task) of Silverman and Eals' (1992) task to evaluate object location memory. This task consists of a stimulus array and a response array of 27 objects on a white sheet of paper. The response array contains the same objects as the stimulus array, but 14 were switched from
Sex differences in location recognition accuracy
We analyzed the results using a two-way analysis of variance (ANOVA), using group (three minutes, one week) and sex (male, female) as between-subjects variables. The dependent measure was the total number of correct identifications in the object location memory task. A significant main effect of sex was observed [F (1, 80) = 6.07, p < 0.05], qualified by an interaction between group and sex [F (1, 80) = 7.80, p < 0.01]. Post hoc analysis (Ryan's) revealed a female advantage in the three-minute memory
Discussion
This study investigated sex differences in long-term retention of object location, in addition to differences in the ability to recall location-exchanged and location-maintained objects, as presented in results of Silverman and Eals' object location memory test. The hunter–gatherer theory holds that successful gathering would have entailed locating edible plants among diverse configurations of vegetation and then finding them again in subsequent growing seasons (Eals and Silverman, 1994,
Acknowledgements
This study was supported by a Grant-in-Aid for Young Scientists (Start-up) No. 18830064 from the Japan Society for the Promotion of Science.
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