In this study we sought initial insight into the process by which a person passes from an oriented to a disoriented state, with respect to the immediate environment. We sought to challenge participants’ capacity to remain oriented with a task in which they experienced sequences of rotations without visual and auditory input. This study was effective in demonstrating a gradual decrease in the ability to point to specific target headings across successive turns in this task. Both variable error and absolute constant error in the pointer responses increased with successive turns. The Turn Number manipulation was evidently effective in challenging participants’ ability to remain oriented, and by the final turns performance across participants in the 200 Degree, Home condition met established criteria indicating that full disorientation had occurred. Although participants became increasingly less confident of their pointer responses over successive turns, error and confidence were not highly correlated on a trial by trial basis. Finally, in addition to the gradual loss of orientation described above, cases in which disorientation seems to have occurred abruptly were identified as well.
The analysis showing that criteria for disorientation were met by the final turns of the 200 Degree, Home condition is noteworthy for several reasons. First, it provides evidence that the current study included the state of full disorientation. Second, it suggests that in the current paradigm, a considerable amount of passive, blind rotation (5, 200° turns) is necessary to induce such a state. Of course, the rotation acceleration rates are important factors in the accuracy of the signals generated by the vestibular system, which is insensitive to very low rates. Considerably slower rates than those used here would likely result in full disorientation occurring sooner. Finally, it is worth noting that when incremental error (accruing only over the most recent turn) was analyzed, performance did not reach criteria for disorientation by the final turns of the 200 Degree, Home condition. This indicates that even in a state of full disorientation, participants were able to perceive ongoing rotations with some degree of accuracy.
The process of becoming disoriented with respect to the immediate environment may be examined further in light of current results. Consider the results for trials on which participants were required to indicate what their heading had been at the beginning of the current turn (Turn Beginning condition). Variable error on these trials increased with successive turns regardless of whether the turns were 70° or 200° in magnitude. Participants were required on these trials to report their perception of the current turn. So, while we have shown that the capacity for perceiving turns never totally broke down, this result implies that it did decrease with successive turns.
Previous research indicates possible mechanisms by which this decrease in perceptual capacity might occur. For example, Barr (1976)
showed that visual preview boosted the gain of the vestibular ocular reflex (VOR) occurring in subsequent blind rotation. Using a paradigm similar to that used in the current study, Arthur, Philbeck and Chichka (in press) showed that visual preview resulted in more precise pointing responses after blind rotations. Thus, in the current study, processes involved in the perception of blind rotation may benefit more from signals (e.g., eye movements) related to the VOR on initial turns than on later turns due to the relative recency of visual preview. Rieser (1999)
has suggested that stored environmental representations might support imagined visual flow, which could contribute to path integration processes and thus to the maintenance of orientation over blind motion. Current results may reflect the deterioration of the stored visual and spatial information that supports imagined visual flow, or more generally, environmental flow. (See Arthur, et al. for a more comprehensive discussion of the role of stored environmental representations in the deterioration of perceptual abilities over blind rotation.)
Alternatively, current results may reflect deteriorating contributions from vestibular and somatosensory systems that are independent of stored environmental information. Future research involving more rigorous controls would be informative in this regard. For example, eye movement, and head on neck movement might be controlled in order to better isolate the contribution of vestibular signals to perception of blind rotation. The importance of stored visual information in explaining the observed decrease in perceptual capacity might be bolstered if that decrease could be specifically tied to eye movement.
Consider next the results for trials on which participants were required to indicate what their heading had been at the beginning of the current trial (Home condition). Why might variable error in this condition have been higher over all, and increased more dramatically across turns than in the Turn Beginning condition? One possible factor is that the egocentrically defined direction of the target was constant within trials of the Turn Beginning condition, but varied in the Home condition. It is quite possible that this egocentric consistency results in lower variable error. This possibility could be explored by including experimental trials that comprise series of turns of different sizes, and thus varying egocentric target directions. Another possible factor arises if we consider that the target direction in the Home condition was constant with regard to an allocentric, or environmentally defined frame of reference. Because the target remains fixed relative to the environment in the Home condition, it seems reasonable that the task would be performed by the common process of attempting to maintain orientation relative to salient environmental cues, such as a representation of the surrounding room (e.g., Hermer & Spelke, 1994
; Shelton & McNamara, 2001
). The Turn Beginning condition however, may favor processes that rely relatively less on intact environmental representations, and more directly on vestibular and somatosensory signals. For example, participants might use the pointer to simply “undo” the most recent turn based on immediate sensory signals. Thus, greater error in the Home than the Turn Beginning condition might reflect a greater dependence on eroding environmental representations in the Home condition.
Other possible explanations of why error was greater in the Home than the Turn Beginning condition arise depending on how the difference between the two conditions is conceptualized. We may reasonably equate the processes contributing to angular self motion updating over each individual turn in the Home and Turn Beginning conditions if we assume that participants are continuously updating and maintaining the single target heading only (Fujita, Loomis, Klatzky, & Gollege, 1990
; Muller & Wehner, 1988
). In this conception, the representation of the target heading would have no associated trace of the history of rotation, or at least none extending further back than the most recent turn. However, Loomis, et al. (1993)
have shown evidence that over blind navigation, humans do not simply update a single homing vector (the distance and relative direction from themselves to their starting positions) but that they also construct a record of the path traveled. If a similar “rotation history” is encoded in the current study, it seems reasonable that such encoding would be more difficult in the Home condition, as the relevant history involves the entire series of turns rather than just the most recent. To the degree that this history is relied upon in providing pointing responses then, the greater degree of complexity involved in updating, maintaining and retrieving this history in the Home condition might result in a greater degree of pointing error. This explanation suggests that the complexity of integrating an increasing amount of self motion history may also play a role in the process of becoming disoriented.
Results showing a decrease in confidence over successive rotations, as more time passes and more motion occurs without intervening perceptual support, are not surprising. Results showing greater decreases in confidence over turns in the Home than in the Turn Beginning condition also make sense. In the Home condition, over the course of any given turn (other than the very first), the uncertainty that would accrue to the target heading would be added to that already associated with the target heading previously indicated. Alternatively, in the Turn Beginning condition, the target heading may be established with greater certainty prior to each turn (as “forward”), and whatever uncertainty accrues over the turn would thus be added to a lower “baseline uncertainty”.
In the current study, the correlation between confidence and accuracy, examined across participants on a trial by trial basis was not strong. The correlation between confidence and constant error was very close to zero (.02). This result appears to provide experimental evidence that there is little relationship between phenomenological and de facto disorientation. However, a significant, if not overwhelming correlation was observed between confidence and variable error (−.39). It is impossible to determine, based on the current study, whether lower confidence may have caused greater variable error, been caused by other factors that also caused greater error, or both. Further research is needed to clarify the complex relationship between confidence and pointing performance.
Regarding constant error (incremental error
in the Home condition), there was a significant effect of Turn Number for both Home and Turn Beginning conditions. Notably, constant error was increasingly negative with successive turns for 70° trials, and increasingly positive with successive turns for 200° trials. In other words, over successive rotations, 70° turns were increasingly over
estimated, while 200° turns were increasingly under
estimated. This pattern makes sense when we remember that the average turn size across the entire study was 135°. Thus, participants responded as if both turn sizes were closer than they actually were to the mean turn size for the study as a whole. This apparent regression to the mean phenomenon, or range effect, which has been observed in previous work (e.g., Klatzky et al., 1990
; Poulton, 1977
), may have become increasingly apparent over successive turns because of the simultaneously decreasing influence of other factors which might have contributed to more veridical estimations of turn size (e.g., environmental flow). The relationship between sensory uncertainty and magnitude of the range effect is considered in some depth by Jurgens and Becker (2006)
. It is unclear, in the present case, whether this phenomenon reflects a cognitive level response bias formed as a result of experience with the range of turn sizes used in the current study, or a tendency occurring in lower level perceptual processing whereby small turns are actually perceived as larger than they are, and large turns as smaller, regardless of the actual mean of the turns (Klatzky, et al., 1999
). In any case, to guard against the former possibility, turn size might be included as a between subjects factor in future efforts.
Beyond revealing this apparent range effect, the constant error data from this study are somewhat less informative regarding tendencies humans may have to over- or underestimate blind rotation as they become increasingly disoriented.3
Prior research has provided some evidence that blindfolded participants tend to underestimate whole body rotations (Blouin, et al., 1995a
). However, subsequent work by Mergner, Nasios, Maurer and Becker (2001)
has shown that such apparent rotation misperceptions can vary depending on a number of variables such as a) how perception of the rotation is assessed (e.g., pointing, eye movement, target adjustment), b) target eccentricity, c) the relative involvement of retinal, orbital and neck afferent signals, and critically, and d) the rate of acceleration (the vestibular apparatus has high-pass frequency characteristics and is insensitive to very low accelerations).
Another goal of the study was to show that occasional abrupt failures in pointing performance occurred in conjunction with the gradual decrease in performance. The study was also effective in this respect. We identified a small number of instances in the Home condition in which performance was very poor and showed that the large error observed in these instances did not accumulate gradually over previous turns. Thus, our results suggest two routes from the oriented to the disoriented state. On one hand, one may gradually lose the capacity to localize objects in the surrounding environment. The analysis showing that performance across participants did not reach criteria for disorientation until the final 200° turns of the Home condition suggests that this gradual route to disorientation was most common, at least in the particular circumstances of this paradigm. On the other hand, one may abruptly lose that capacity. As expected, results showed that this occurred far more frequently in the 200° than in the 70° Turn Size condition. However, unexpectedly, the incidence of such abrupt losses of orientation did not increase with successive turns, wherein perceptual demands had accumulated and visual support was more remote. This raises the possibility that increasing perceptual demands and decaying visual memory are not always the primary causes of abrupt disorientation. Non-spatial cognitive processes may also be a factor. For example, all or some of the abrupt losses of orientation observed here may have resulted from lapses in attention. It is also possible that confidence in the coupling between heading direction and a deteriorating environmental representation reaches a critical minimum at which point the old coupling is abandoned and a new one is adopted arbitrarily, or on the basis of real or imagined perceptual cues. Finally, abrupt losses of orientation were not concentrated in the condition in which disorientation appears to have occurred across participants (the final 200° turns of the Home condition). This supports the conclusion that the two routes to disorientation, gradual and abrupt, are distinct.
To sum up what we have learned about the process of becoming disoriented, first, over whole body rotation, in the absence of visual and auditory input, the ability to perceive that rotation gradually decreases. However, the ability to perceive that movement relative to egocentrically consistent targets decreases less dramatically than the ability to perceive that movement relative to allocentrically consistent targets. Possible mechanisms in the loss of orientation were discussed in light of these results. Second, while correlations between confidence and degree of objective orientation are very weak in this paradigm, there is a significant correlation between confidence and precision of responses. Finally, we have shown evidence for occasional abrupt losses of orientation, suggesting an alternative route to disorientation that may involve different mechanisms. Future studies involving disorientation may benefit from the preliminary steps, taken here, towards unpacking this complex topic.