Avraamides (2004) Use of cognitive versus perceptual heading during imagined locomotion depends on the response mode

Three experiments investigated whether the systematic errors previously observed in a triangle-completion task were caused by failures to form and update a cognitive heading or by use of perceived heading (even though an updated cognitive heading was available) during the response. These errors were replicated when participants indicated the origin of triangular paths they had imagined walking by turning their bodies toward the origin, but not when they responded verbally. The results indicate that participants are capable of updating their cognitive heading using imagined movements and suggest that the systematic errors previously observed were a result of the strong attachment of responses such as turns to a perceptual representation of the physical body. Navigation relies on updating one’s position and orientation with respect to the environment. The central nervous system makes use of many sources of information in performing spatial updating. For example, perceptual information about the position of landmarks in the immediate environment can be used to ‘‘fix’’ one’s position (e.g., by triangulation). When landmarks are absent, navigation can be carried out by means of path integration (Loomis, Klatzky, Golledge, & Philbeck, 1999). In this case, information about one’s translations and turns are used to determine heading and distance from the origin of travel; this information can be external (e.g., optic flow) or body based (e.g., proprioception). The abundance of information available for spatial updating suggests that given corresponding sensory capabilities, navigators should have considerable capability to update their position and orientation while moving in space even without vision. Indeed, empirical findings suggest that this is the case (e.g., Loomis et al., 1999; Philbeck, Loomis, & Beall, 1997; Rieser, Guth, & Hill, 1986; Simons & Wang, 1998). For example, Philbeck et al. (1997) asked participants to walk with eyes closed to previously seen targets using direct or indirect paths that were specified after vision was occluded. Participants could perform the task very accurately regardless of the path taken, suggesting that they were able to update their position on the basis of information available from self-directed movement. Similarly, Rieser et al. (1986) had participants learn a layout of objects from one standpoint and then point to them, while blindfolded, from that standpoint or a novel one. Pointing latency did not differ between the standpoints, suggesting that participants were able to update the layout while moving (blindfolded) to the novel position. Although successful updating occurs with physical movements, imagined movements typically lead to impaired performance, indicating failure to update equivalently (e.g., Farrell & Robertson, 1998; Presson & Montello, 1994; Rieser, 1989; but see Wraga, in press). For example, in a study by Rieser (1989), which paralleled that of Rieser et al. (1986) but with rotations, performance was slower for imagined rotations than for physical rotations, and response latencies increased as a function of the angular deviation of the target from the participant’s physical facing direction. A possible explanation is that imagined movements lack any correlation with vestibular signals or afferent and efferent proprioception. As many researchers have posited (e.g., Rieser, 1989), without direct sensory cues, spatial updating requires effortful cognitive processing. In light of the evidence for impaired performance with imagined movements, Klatzky, Loomis, Beall, Chance, and Golledge (1998) argued for a distinction between two internal representations of heading: Perceived heading refers to what one experiences to be one’s facing direction, whereas cognitive heading is any heading that one Journal: PSCI H Disk used ED: Saravan Pgn by: ananth Article: 692 Pages:6 (col.fig.: NIL) Despatch Date: 23/3/2004 Address correspondence to Marios N. Avraamides, Department of Psychology, University of California, Santa Barbara, CA 931069660; e-mail: [email protected]. In most cases, perceived heading is the same as a person’s physical heading. However, there are ways to dissociate the two (e.g., by using virtual reality) so that a person feels he or she is facing a direction that is different from his or her actual facing direction. PSYCHOLOGICAL SCIENCE Volume 15—Number 6 403 Copyright r 2004 American Psychological Society B W U S P S C I 6 9 2 . P D F 2 3 M a r 0 4 1 5 : 7 1 2 1 7 2 2 B y t e s 6 P A G E S UN CO RR EC TE D PR OO F can adopt through imagination, including a heading adopted for purposes of a task that requires reasoning from a perspective other than one’s own. Whereas perceived heading is updated by perceptual processes during physical movement, updating cognitive heading is believed to require effortful cognitive processing. Klatzky et al. (1998) used a triangle-completion task to examine the updating of perceived heading under conditions of physical movement and imagined movement induced in various ways. On each trial, participants experienced a path consisting of two outbound legs (Leg 1 and Leg 2) and an intervening turn (Turn 1). At the end of the outbound path, participants were asked to produce, while standing, the turn that someone who walked the path would make in order to face the path’s origin (Turn 2). This response measure was chosen because it makes use of the physical body, and was therefore believed to be governed by perceived heading. In a describe condition, blindfolded participants listened to descriptions specifying Legs 1 and 2 in meters and Turn 1 in degrees. In a walk condition, blindfolded participants were guided over the outbound path by the experimenter. In a watch condition, participants watched an experimenter walk the outbound path. Two additional conditions involved experiencing simulated movements (specified by optic flow in a virtual environment), accompanied by either real or simulated turns (real-turn and visual-turn conditions, respectively). Results revealed that only when real rotations were performed (i.e., walk and real-turn conditions) did participants perform Turn 2 accurately. In the remaining conditions, participants systematically overturned by the value of Turn 1. For example, if Turn 1 was 901 and the correct Turn 2 was 1351, participants tended to turn 2251 instead. Figure 1 demonstrates the task. Suppose a participant in the describe condition is standing at the origin with a perceived heading aligned with Leg 1 (which we designate as 01) and then imagines walking three steps forward, turning 901 to the right, and walking another two steps. If the participant forms and updates a cognitive representation of heading, then after executing Turn 1, he or she should have a cognitive heading that differs in orientation from perceived heading by the value of Turn 1. In our example, cognitive heading is 901. To make a response, the participant needs to compute Turn 2, or the relative bearing, defined as follows: relative bearing 1⁄4 return bearing current heading ð1Þ (The return bearing and the current heading must be defined with respect to a common reference direction—in our example, aligned with Leg 1.) The return bearing is the direction of home from the end of Leg 2. The participant should have two current headings available, cognitive heading and perceived heading. In our example, the return bearing is 2141, and the current heading the participant is supposed to use in the computation is cognitive heading, or 901; hence, the correct Turn 2 is 1241. The participant, however, incorrectly executes a turn of 2141, which is greater than the correct response by the value of Turn 1. The tendency to overrespond by the value of Turn 1 indicates that Equation 1, using cognitive heading for the current heading, is not applied. If the cognitive heading has been formed, updated, and used in the computation, the error should not be observed. We consider two hypotheses that might account for the error pattern. First, there might be only one heading available, perceived heading, which must be used to compute the relative bearing and make the response turn. (A computationally equivalent idea is that there is a second heading, cognitive heading, but it is updated only if the perceptual heading changes.) This hypothesis would predict the observed errors, but it is problematic given the evidence that people can—with cognitive effort—adopt a cognitive heading different from their physical one. A second hypothesis is that although participants have a cognitive heading and update it when experiencing the outbound path, they fail to take it into account when computing Turn 2. In terms of Equation 1, participants subtract the value of perceived heading, instead of that of cognitive heading, from the return bearing. We suspected that the body-referred nature of the response mode in the study by Klatzky et al. (1998) could have induced such an error. Recent evidence (Wraga, in press) indicates that body-referred responses, particularly manual pointing, are difficult to use from imagined perspectives. The coupling of the response mode in Klatzky et al. (1998) with the physical body could have induced participants to use perceived heading to compute Turn 2. In order to assess this possibility, in the present study we repeated two conditions of Klatzky et al. (1998) while using a response measure that we believe relies less strongly on perceived heading. Specifically, we had participants respond verbally, by indicating the direction of Turn 2 and its extent in degrees, after performing the task as in the watch and describe conditions of Klatzky et al. It appears that spatial language (i.e., verbal report) can be used more flexibly from imagined perspectives than bodyreferred responses can be because it is not bound to the physical body (De Vega & Rodrigo, 2001; Wraga, in press; see also Avraamides, in press). In everyday life, people often use spatial language from Fig. 1. Schematic representation of an example path. The participant is standing at the origin with a perceived heading (Headingp) aligned with Leg 1 (designated as 01) and then imagines walking three steps forward, turning 901 to the right, and walking another two steps. The task is to turn to face the direction in which the origin would be. Participants typically do not account for cognitive heading (Headingc) in calculating their response, and consequently overshoot the correct response of a right turn of 1241. PSCI : 692 404 Volume 15—Number 6 Cognitive Versus Perceptual Heading B W U S P S C I 6 9 2 . P D F 2 3 M a r 0 4 1 5 : 7 1 2 1 7 2 2 B y t e s 6 P A G E S UN CO RR EC TE D PR OO F perspectives other than their own (e.g., when giving directions to others). If the systematic errors reported by Klatzky et al. (1998) were induced by the motor response, and do not reflect the lack of an updated cognitive heading, then no such errors would be expected with verbal responses. In contrast, if the errors were due to participants’ failure to form and develop a cognitive heading, then systematic errors would be present with both body turns and verbal responses.