Steve E. Avons

Using Behavioral Realism to Estimate Presence: A Study of the Utility of Postural Responses to Motion Stimuli

We recently reported that direct subjective ratings of the sense of presence are potentially unstable and can be biased by previous judgments of the same stimuli (Freeman et al., 1999). Objective measures of the behavioral realism elicited by a display offer an alternative to subjective ratings. Behavioral measures and presence are linked by the premise that, when observers experience a mediated environment (VE or broadcast) that makes them feel present, they will respond to stimuli within the environment as they would to stimuli in the real world. The experiment presented here measured postural responses to a video sequence filmed from the hood of a car traversing a rally track, using stereoscopic and monoscopic presentation. Results demonstrated a positive effect of stereoscopic presentation on the magnitude of postural responses elicited. Posttest subjective ratings of presence, vection, and involvement were also higher for stereoscopically presented stimuli. The postural and subjective measures were not significantly correlated, indicating that nonproprioceptive postural responses are unlikely to provide accurate estimates of presence. Such postural responses may prove useful for the evaluation of displays for specific applications and in the corroboration of group subjective ratings of presence, but cannot be taken in place of subjective ratings.

Effects of Sensory Information and Prior Experience on Direct Subjective Ratings of Presence

We report three experiments using a new form of direct subjective presence evaluation that was developed from the method of continuous assessment used to assess television picture quality. Observers were required to provide a continuous rating of their sense of presence using a handheld slider. The first experiment investigated the effects of manipulating stereoscopic and motion parallax cues within video sequences presented on a 20 in. stereoscopic CRT display. The results showed that the presentation of both stereoscopic and motion parallax cues was associated with higher presence ratings. One possible interpretation of Experiment 1 is that CRT displays that contain the spatial cues of stereoscopic disparity and motion parallax are more interesting or engaging. To test this, observers in Experiment 2 rated the same stimuli first for interest and then for presence. The results showed that variations in interest did not predict the presence ratings obtained in Experiment 1. However, the subsequent ratings of presence differed significantly from those obtained in Experiment 1, suggesting that prior experience with interest ratings affected subsequent judgments of presence. To test this, Experiment 3 investigated the effects of prior experience on presence ratings. Three groups of observers rated a training sequence for interest, presence, and 3-Dness before rating the same stimuli as used for Experiments 1 and 2 for presence. The results demonstrated that prior ratings sensitize observers to different features of a display resulting in different presence ratings. The implications of these results for presence evaluation are discussed, and a combination of more-refined subjective measures and a battery of objective measures is recommended.

The Word-length Effect and Disyllabic Words

Three experiments compared immediate serial recall of disyllabic words that differed on spoken duration. Two sets of long- and short-duration words were selected, in each case maximizing duration differences but matching for frequency, familiarity, phonological similarity, and number of phonemes, and controlling for semantic associations. Serial recall measures were obtained using auditory and visual presentation and spoken and picture-pointing recall. In Experiments 1a and 1b, using the first set of items, long words were better recalled than short words. In Experiments 2a and 2b, using the second set of items, no difference was found between long and short disyllabic words. Experiment 3 confirmed the large advantage for short-duration words in the word set originally selected by Baddeley, Thomson, and Buchanan (1975). These findings suggest that there is no reliable advantage for short-duration disyllables in span tasks, and that previous accounts of a word-length effect in disyllables are based on accidental differences between list items. The failure to find an effect of word duration casts doubt on theories that propose that the capacity of memory span is determined by the duration of list items or the decay rate of phonological information in short-term memory.

Serial position curves in short‐term memory: Functional equivalence across modalities

Four experiments investigated item and order memory for sequences of seen unfamiliar faces and heard nonwords. Experiments 1 and 3 found bowed serial position curves using the serial reconstruction test of order with faces and nonwords, respectively. Experiments 2 and 4 found limited recency, no primacy, and above chance performance on all items using a two‐alternative forced choice (2AFC) test of item recognition, again with faces and nonwords. These results suggest that the different serial position curves typically found using traditional paradigms for exploring visual and verbal short‐term memory are due to differences in the methods used rather than modality‐specific mechanisms.

One process is not enough! A speed-accuracy tradeoff study of recognition memory

Speed-accuracy tradeoff (SAT) methods have been used to contrast single- and dual-process accounts of recognition memory. In these procedures, subjects are presented with individual test items and are required to make recognition decisions under various time constraints. In this experiment, we presented word lists under incidental learning conditions, varying the modality of presentation and level of processing. At test, we manipulated the interval between each visually presented test item and a response signal, thus controlling the amount of time available to retrieve target information. Study— test modality match had a beneficial effect on recognition accuracy at short response-signal delays (≤300msec). Conversely, recognition accuracy benefited more from deep than from shallow processing at study only at relatively long response-signal delays (≥300 msec). The results are congruent with views suggesting that both fast familiarity and slower recollection processes contribute to recognition memory.

Toward a Unified Account of Spacing Effects in Explicit Cued-Memory Tasks

Memory for repeated items improves when presentations are spaced during study. This effect is found in memory tasks using different types of material, paradigms, and participant populations. Although several explanations have been proposed, none explains the presence of spacing effects in cued-memory tasks for unfamiliar stimuli. Two experiments assessed the spacing effect on a yes-no recognition-memory task using nonwords and words as targets. The main results showed that changing the font between repeated occurrences of targets at study removed the spacing effect for nonwords only. A 3rd experiment using lexical decision showed that the font manipulation reduced repetition priming of nonwords when items were repeated at Lag 0. These results suggest that short-term perceptual priming supports spacing effects in cued-memory tasks for unfamiliar stimuli.

Dynamic visual noise: No interference with visual short‐term memory or the construction of visual images

The effects of dynamic visual noise (DVN) and static visual noise (SVN) were assessed on a visual short‐term memory (STM) task, in which a matrix pattern was briefly presented and followed by a recognition test, and a new, cumulative imagery task, in which the elements of a pattern were presented one at a time, and participants were asked to imagine the pattern formed by displaying all the elements together. When presented during the retention interval neither DVN nor SVN affected visual STM performance. The cumulative imagery task was not affected by visual noise presented either during the retention interval or concurrently while the elements of the pattern were shown. Increasing the spatial demands of the task decreased performance, but did not interact with type of visual noise. The results (1) show that DVN in relatively short bursts does not interfere with visual STM, (2) argue against the view that DVN impairs the localisation of pattern elements, and (3) provide no support for the view that concurrent DVN mandatorily disrupts the formation of visual images. The implications for studies of visual imagery and visual STM are discussed.

Spacing effects in cued-memory tasks for unfamiliar faces and nonwords

Memory for repeated items improves as the interval between repetitions in a list increases (the spacing effect). This study investigated the spacing effect in recognition memory and in a frequency judgment task for unfamiliar target faces that were repeated in the same or in a different pose during incidental learning. Changing the pose between prime and probe trials reduced perceptual repetition priming in a structural discrimination task and also reduced the spacing effect in a subsequent unexpected recognition memory task. Three further experiments confirmed that the spacing effect in recognition memory (Experiments 2 and 4) or frequency judgment (Experiment 3) was reduced when the pose was changed between repeated presentations at study. Similarly, with nonwords as targets (Experiment 5), changing the font between repeated occurrences of targets at study removed the spacing effect in a subsequent unexpected recognition memory test. These results are interpreted to support the view that short-term perceptual repetition priming underlies the spacing effect in explicit cuedmemory tasks for unfamiliar nonsense material.

Reversing the picture superiority effect: A speed—accuracy trade-off study of recognition memory

Speed—accuracy trade-off methods have been used to contrast single—and dual-process accounts of recognition memory. With these procedures, subjects are presented with individual test items and required to make recognition decisions under various time constraints. In three experiments, we presented words and pictures to be intentionally learned; test stimuli were always visually presented words. At test, we manipulated the interval between the presentation of each test stimulus and that of a response signal, thus controlling the amount of time available to retrieve target information. The standard picture superiority effect was significant in long response deadline conditions (i.e., ≥2,000 msec). Conversely, a significant reverse picture superiority effect emerged at short response-signal deadlines (<200 msec). The results are congruent with views suggesting that both fast familiarity and slower recollection processes contribute to recognition memory. Alternative accounts are also discussed.

The dangers of taking capacity limits too literally

The empirical data do not unequivocally support a consistent fixed capacity of four chunks. We propose an alternative account whereby capacity is limited by the precision of specifying the temporal and spatial context in which items appear, that similar psychophysical constraints limit number estimation, and that short term memory (STM) is continuous with long term memory (LTM).