**6. General discussion**

In this study we investigated the influences of simultaneous and sequential vision on human spatial navigation by using two classic procedures adapted from animal research. A virtual model of the Morris water maze (Morris, 1981) was used in the task, in which participants had to locate a hidden underwater platform in the pool. Experiments were designed in order to analyze in test trials the effect of the removal of one of the landmarks (Experiment 1) and the influence of increasing the distance between them (Experiment 2). The time spent by the participants in each sector of the pool was registered and taken as a dependent variable in data analysis.

In Experiment 1 we verify that participants with simultaneous vision spent more time in the relevant sector (8th) in comparison to other sectors of the pool. However, participants with sequential vision spent approximately the same time in the relevant and adjacent sectors. These results indicate that simultaneous vision compared to sequential vision improves spatial navigation in a virtual environment.

Similarly, in Experiment 2 participants with simultaneous vision also spent more time in the relevant sector (8th) compared to the other sectors in both conditions (expanded and nonexpanded landmarks). But when participants with sequential vision were submitted to the condition of expanded landmarks they spent more time in the 10th and 6th in comparison to the 7th, 8th and 9th sectors. For the case in which participants with sequential vision were submitted to non-expanded landmarks (90o), they spent more time in the relevant (8th) and adjacent (7th and 9th) sectors.

As a whole, these results indicate that participants use different strategies depending on the visual condition. Participants submitted to simultaneous vision tended to navigate directly to the relevant sector (8th), indicating that they used a "middle rule" strategy based on a configural learning. However, participants with sequential vision submitted to the procedure of the removal of one landmark (Experiment 1) spent more time in the three sectors between the two landmarks (7th, 8th and 9th), suggesting that they navigate from one landmark to another based on an elemental learning. The latter finding is reinforced by the observation that when the distance between the landmarks was increased, participants

Finally, an analysis of the variance with "groups" (simultaneous vs. sequential vision) and "types of test" (expanded vs. non-expanded landmarks) as factors was conducted. The time in the 0th sector (starting point) was taken as the dependent variable. Results revealed a statistically significant effect of "groups" [F(1,66)= 5.63; p < .021] and "types of test" [F(1,66)= 4.106; p < .047] as well as an interaction between them [F(1,66)= 5.879; p < .018].

A *post hoc* analysis of the interaction indicated that, only for the group with simultaneous vision, the distance between the landmarks affected the time spent at the starting point (Figure 6). In such cases, participants submitted to expanded landmarks (150º) spent more time (mean = 6.32 s) compared to those submitted to non-expanded landmarks (90º) (mean = 2.50 s). We can consider two possible explanations for these results. On the one hand, the change *per se* in the distance between landmarks promoted a decrease in the generalization of the response, and on the other, when the landmarks are further apart, the time to define

In this study we investigated the influences of simultaneous and sequential vision on human spatial navigation by using two classic procedures adapted from animal research. A virtual model of the Morris water maze (Morris, 1981) was used in the task, in which participants had to locate a hidden underwater platform in the pool. Experiments were designed in order to analyze in test trials the effect of the removal of one of the landmarks (Experiment 1) and the influence of increasing the distance between them (Experiment 2). The time spent by the participants in each sector of the pool was registered and taken as a

In Experiment 1 we verify that participants with simultaneous vision spent more time in the relevant sector (8th) in comparison to other sectors of the pool. However, participants with sequential vision spent approximately the same time in the relevant and adjacent sectors. These results indicate that simultaneous vision compared to sequential vision improves

Similarly, in Experiment 2 participants with simultaneous vision also spent more time in the relevant sector (8th) compared to the other sectors in both conditions (expanded and nonexpanded landmarks). But when participants with sequential vision were submitted to the condition of expanded landmarks they spent more time in the 10th and 6th in comparison to the 7th, 8th and 9th sectors. For the case in which participants with sequential vision were submitted to non-expanded landmarks (90o), they spent more time in the relevant (8th) and

As a whole, these results indicate that participants use different strategies depending on the visual condition. Participants submitted to simultaneous vision tended to navigate directly to the relevant sector (8th), indicating that they used a "middle rule" strategy based on a configural learning. However, participants with sequential vision submitted to the procedure of the removal of one landmark (Experiment 1) spent more time in the three sectors between the two landmarks (7th, 8th and 9th), suggesting that they navigate from one landmark to another based on an elemental learning. The latter finding is reinforced by the observation that when the distance between the landmarks was increased, participants

the correct vector and direction increases.

dependent variable in data analysis.

adjacent (7th and 9th) sectors.

spatial navigation in a virtual environment.

**6. General discussion** 

with sequential vision spent more time in the sectors near the landmarks (6th and 10th). This pattern of results reveals that participants adopted two different strategies. The "middle rule" strategy takes into account the egocentric direction to determine the correct bisector between the starting point and the landmarks, while the "landmark to landmark" strategy takes into account the exocentric direction.

In the context of visual control of the action, Goodale and Humphrey (2001) state that perceptual tasks differ from motor tasks as a consequence of information processing in two independent neural pathways: the ventral (related to perception, e.g. object recognition) and the dorsal (related to directed action, e.g. blind walking). Dissociation between perception and action can be found in many studies (Goodale & Milner, 1992; Loomis et al., 1992; Smeets & Brenner, 1995; Philbeck et al., 1997; Fukusima et al., 1997; Kelly, Loomis & Beal, 2004; Kudoh, 2005). However, there is also evidence against this dissociation, with many papers trying to reconcile the pathways (Kugler & Turvey, 1987; Goodale & Humphrey, 2001, Norman, 2002). In this study, results might sustain the hypothesis of the dissociation between perception and action, with the "middle rule" being related to a perceptual strategy, while the navigation from "landmark to landmark" implies an action strategy.

We verified that the expanding landmarks test helped to clarify the strategies adopted by the participants with sequential vision. According to Sutherland & Rudy (1989), if the responses of the participants were based on an elemental learning, they should present a good performance in the test with two landmarks, but a worse performance in the test with one landmark. However, if the responses of the participants are based on configural learning, they should present a good performance in both types of test (removal and expanding procedure). If we apply those criteria to the data, we conclude that the group with sequential vision adopted an elemental strategy, whereas the group submitted to simultaneous vision adopted a configural one. However, we should note that these authors made this assertion in the context of discriminatory learning and it has not been applied to a spatial task until now.

These results differ from those obtained by MacDonald et al. (2004), who pointed out that human adults use a "middle rule" strategy, but that children and other primates do not. Our results suggest that only participants with simultaneous vision used a "middle rule" strategy, while participants with sequential vision employed a strategy of advancing from one landmark to another. In other words, navigation with simultaneous vision follows an egocentric vector directed to the middle of the landmarks, while sequential vision follows an exocentric vector that connects landmark to landmark.

The simultaneous visual access of the participants to the relevant information enables them to integrate the spatial relation easier and promotes a configural encoding which, in turn, allows the use of "middle rule" strategy. The visual access to only one landmark at a time makes the learning of global spatial relations difficult but promotes the elemental relationship between landmarks, enabling participants to apply the "connecting landmarks rule". However, more research is necessary in order to conclude whether these results could be attributed to general rules in spatial navigation or to the extensive training in the sequential condition.

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