Sensory memory of illusory depth in structure-from-motion

When multistable displays (stimuli consistent with two or more equally plausible perceptual interpretations) are presented intermittently, their perceptions are stabilized by sensory memory. Independent memory traces are generated not only for different types of multistable displays (Maier, Wilke, Logothetis, & Leopold, Current Biology 13:1076–1085, 2003), but also for different ambiguous features of binocular rivalry (Pearson & Clifford, Journal of Vision 4:196–202, 2004). In the present study, we examined whether a similar independence of sensory memories is observed in structure-from-motion (SFM), a multistable display with two ambiguous properties. In SFM, a 2-D planar motion creates a vivid impression of a rotating 3-D volume. Both the illusory rotation and illusory depth (i.e., how close parts of an object appear to the observer) of an SFM object are ambiguous. We dissociated the sensory memories of these two ambiguous properties by using an intermittent presentation in combination with a forced-ambiguous-switch paradigm (Pastukhov, Vonau, & Braun, PLoS ONE 7:e37734, 2012). We demonstrated that the illusory depth of SFM generates a sensory memory trace that is independent from that of illusory rotation. Despite this independence, the specificities levels of the sensory memories were identical for illusory depth and illusory rotation. The history effect was weakened by a change in the volumetric property of a shape (whether it was a hollow band or a filled drum volume), but not by changes in color or size. We discuss how these new results constrain models of sensory memory and SFM processing.     

Displacement in depth: Representational momentum and boundary extension

Memory for targets moving in depth and for stationary targets was examined in five experiments. Memory for targets moving in depth was displaced behind the target with slower target velocities (longer ISIS and retention intervals) and beyond the target with faster target velocities (shorter ISIS and retention intervals), and the overall magnitude of forward displacement for motion in depth was less than the overall magnitude of forward displacement for motion in the picture plane. Memory for stationary targets was initially displaced away from the observer, but memory for smaller stationary targets was subsequently displaced toward the observer and memory for larger stationary targets was subsequently displaced away from the observer; memory for the top or bottom edge of a stationary target was displaced inside the target perimeter. The data are consistent with Freyd and Johnson's (1987) two-component model of the time course of representational momentum and with Intraub et al.'s (1992) two-component model of boundary extension.     

Similarity-guided depth of retrieval: constraining at the front end.

Lee Brooks has done important work to show that categorization often reflects reliance on specific instances rather than on an abstract representation. His work on the advantages of using a diagnostic hypothesis to search medical stimuli has demonstrated how constraining what one looks for influences clinical reasoning. Similarly, cognitive control can be accomplished by constraining memory retrieval in ways that influence interpretation of a memory probe. Here, we report two experiments in which the similarity of study items constrained how test items were interrogated for an immediate memory test and thereby produced differences in the depth of retrieval. A novel procedure that tests foil memory was used to diagnose differences in similarity-guided retrieval depth.     

Memory performance and subject-defined depth of processing

This experiment found that subjects could order a series of classification questions in terms of their relative depth of processing. The subject-defined processing depth was used to predict performance in an incidental learning task which employed the same questions with different subjects. A significant rank correlation was obtained between question depth of processing and stimulus word free recall. These data provide an independent assessment of processing depth and memory performance and thereby satisfy a necessary, but not sufficient condition for the depth-of-processing hypothesis. Little success was achieved, however, in attempting to define the scheme relating processing depth and performance. While memory is related to encoding conditions, the search for the relational scheme continues.     

Representational momentum for rotations in depth: effects of shadings and axis

Representational momentum is a positive memory distortion for an object's final position following the presentation of an implied event (J.J. Freyd, 1987). Positive memory distortions occur when observers accept test positions beyond the final presented position, or forward along the implied trajectory, as the same more readily than positions behind the final position. Four experiments explored implied events depicting rotations about various depth axes in shaded and silhouette conditions. Positive memory distortions were observed for all depth rotations under certain shading conditions, with some differences in the size of the distortion between axes. No directional effects (e.g., right vs. left) were observed. The overall positive memory distortions observed for depth rotations contrasted with the negative distortions previously observed for translation motion in depth (T.L. Hubbard, 1995 ).     

Short-term visual memory for location in depth: A U-shaped function of time

Short-term visual memory was studied by displaying arrays of four or five numerals, each numeral in its own depth plane, followed after various delays by an arrow cue shown in one of the depth planes. Subjects reported the numeral at the depth cued by the arrow. Accuracy fell with increasing cue delay for the first 500 ms or so, and then recovered almost fully. This dipping pattern contrasts with the usual iconic decay observed for memory traces. The dip occurred with or without a verbal or color–shape retention load on working memory. In contrast, accuracy did not change with delay when a tonal cue replaced the arrow cue. We hypothesized that information concerning the depths of the numerals decays over time in sensory memory, but that cued recall is aided later on by transfer to a visual memory specialized for depth. This transfer is sufficiently rapid with a tonal cue to compensate for the sensory decay, but it is slowed by the need to tag the arrow cue’s depth relative to the depths of the numerals, exposing a dip when sensation has decayed and transfer is not yet complete. A model with a fixed rate of sensory decay and varied transfer rates across individuals captures the dip as well as the cue modality effect.     

Overestimation and contraction biases of depth information stored in working memory depend on spatial configuration

Depth perception is essential for effective interaction with the environment. Although the accuracy of depth perception has been studied extensively, it is unclear how accurate the depth information is stored in working memory. In this study, we investigated the accuracy and systematic biases of depth representation by a delayed estimation task. The memory array consisted of items presented at various stereoscopic depth positions, and the participants were instructed to estimate the depth position of one target item after a retention interval. We examined the effect of spatial configuration by comparing the memory performance in the whole-display condition where non-target memory items were present during retrieval with that in the single-display condition where non-target memory items were absent. In the single-display condition, we found an overestimation bias that the depth estimates were farther than the corresponding depth positions defined by disparity, and a contraction bias that the stored depth positions near the observer were overestimated and those far from the observer were underestimated. The magnitude of these biases increased with the number of to-be-stored items. However, in the whole-display condition, the overestimation bias was corrected and the contraction bias did not increase with the number of to-be-stored items. Our findings suggested that the number of to-be-stored items could affect the accuracy of depth working memory, and its effect depended crucially on whether the information of spatial configuration of memory display was available at the retrieval stage.     

Spatial attention based on 2D location and relative depth order modulates visual working memory in a 3D environment

The attentional effect on visual working memory (VWM) has been a heated research topic in the past two decades. Studies show that VWM performance for an attended memory item can be improved by cueing its two-dimensional (2D) spatial location during retention. However, few studies have investigated the effect of attentional selection on VWM in a three-dimensional setting, and it remains unknown whether depth information can produce beneficial attentional effects on 2D visual representations similar to 2D spatial information. Here we conducted four experiments, displaying memory items at various stereoscopic depth planes, and examined the retro-cue effects of four types of cues – a cue would either indicate the 2D or depth location of a memory item, and either in the form of physical (directly pointing to a location) or symbolic (numerically mapping onto a location) cues. We found that retro-cue benefits were only observed for cues directly pointing to a 2D location, whereas a null effect was observed for cues directly pointing to a depth location. However, there was a retro-cue effect when cueing the relative depth order, though the effect was weaker than that for cueing the 2D location. The selective effect on VWM based on 2D spatial attention is different from depth-based attention, and the divergence suggests that an object representation is primarily bound with its 2D spatial location, weakly bound with its depth order but not with its metric depth location. This indicates that attentional selection based on memory for depth, particularly metric depth, is ineffective.     

The relationship between repetition and depth of processing

The relationship between depth of information processing and stimulus repetitions was investigated using a simultaneous category judgment task. Several levels of processing were defined involving (1) physically identical items, (2) physically different but same-name items, (3) different items from the same semantic category, and (4) items from different categories. Stimulus pairs were represented by words and pictures, and each pair was presented one, three, or five times. Response times for categorization judgments increased with the level of processing and decreased with repetitions. Repetitions produced greater facilitation for decisions at deeper levels of processing. In a final incidental recall task, more items were remembered from category-same trials than from same-item trials, but level of processing did not interact with number of presentations. Repetitions produced an equivalent increase in final recall probability for items involved in all decision types, indicating that distributed repetitions can lead to the formation of stronger memory traces at several levels of processing.     

Structure-from-motion: dissociating perception, neural persistence, and sensory memory of illusory depth and illusory rotation

In the structure-from-motion paradigm, physical motion on a screen produces the vivid illusion of an object rotating in depth. Here, we show how to dissociate illusory depth and illusory rotation in a structure-from-motion stimulus using a rotationally asymmetric shape and reversals of physical motion. Reversals of physical motion create a conflict between the original illusory states and the new physical motion: Either illusory depth remains constant and illusory rotation reverses, or illusory rotation stays the same and illusory depth reverses. When physical motion reverses after the interruption in presentation, we find that illusory rotation tends to remain constant for long blank durations (T _blank ≥ 0.5 s), but illusory depth is stabilized if interruptions are short (T _blank ≤ 0.1 s). The stability of illusory depth over brief interruptions is consistent with the effect of neural persistence. When this is curtailed using a mask, stability of ambiguous vision (for either illusory depth or illusory rotation) is disrupted. We also examined the selectivity of the neural persistence of illusory depth. We found that it relies on a static representation of an interpolated illusory object, since changes to low-level display properties had little detrimental effect. We discuss our findings with respect to other types of history dependence in multistable displays (sensory stabilization memory, neural fatigue, etc.). Our results suggest that when brief interruptions are used during the presentation of multistable displays, switches in perception are likely to rely on the same neural mechanisms as spontaneous switches, rather than switches due to the initial percept choice at the stimulus onset.     

Impact of encoding depth on awareness of perceptual effects in recognition memory

Pictorial stimuli are more likely to be recognized if they are the same size, rather than a different size, at study and at test. This size congruency effect was replicated in two experiments in which the encoding variables were respectively undivided versus divided attention and level of processing. In terms of performance, these variables influenced recognition and did not influence size congruency effects. But in terms of awareness, measured by remember and know responses, these variables did influence size congruency effects. With undivided attention and with a deep level of processing, size congruency effects occurred only in remembering. With divided attention and with a shallow level of processing, size congruency effects occurred only in knowing. The results show that effects that occur in remembering may also occur independently in knowing. They support theories in which remembering and knowing reflect different memory processes or systems. They do not support the theory that remembering and knowing reflect differences in trace strength.     

Development of depth perception mediated by motion parallax in unidimensional projections of rotation in depth.

Motion parallax is a composite of five transformations demonstrated to be effective in adult judgments of rotation direction in polar motion projections of a horizontal row of dots rotating in depth. The effectiveness of these transformations as a function of age was tested by presenting six such motion projections to first graders (age = 6 years), seventh graders (age = 13 years), and college students (age = 19 years). Identical age functions were obtained for judged rotation direction from the four motion projections representing (1) Velocity, corresponding to the traditional definition of motion parallax as differential velocity, (2) Velocity plus differences between ratios of instantaneous displacement to instantaneous acceleration for dots on the near and far sides of the rotation axis ($\text{D}\text{A}$ Difference), (3) Velocity, $\text{D}\text{A}$ Difference, and a gradient across the row of $\text{D}\text{A}$ ratios, and (4) all transformations. First graders, unable to use horizontal transformations, performed at chance on these four projections, while older students made correct judgments. Order, separated from Velocity for the first time, resulted in chance performance at all ages, while Direction, also separated from Velocity for the first time, resulted in veridical judgments in only 4 of 24 college students.     

Binocular rivalry and stereoscopic depth perception

An investigation was made of stimulus factors causing retinal rivalry or allowing stereoscopic depth perception, given a requisite positional disparity. It is shown that similar colour information can be “filtered” out from both eyes; that stereopsis is not incompatible with rivalry and suppression of one aspect of the stimulus, and that the strongest cue for perception of stereoscopic depth is intensity difference at the boundaries of the figures in the same direction at each eye. Identity of colour can also act as a cue for stereopsis. The brightness of different monocular figures seen in the stereoscope in different combinations was estimated by a matching technique, and it is suggested that the perceived brightness is a compromise between the monocular brightness difference between figure and ground seen in relation to the binocular fused background, and the mean brightness of the figures. The results are discussed in terms of neurophysiological “on,” “off” and continuous response fibres.     

Practical Memory Concerns of Older Adults

We examine practical memory concerns in a sample of community-dwelling older adults. Participants responded to open-ended questions that were designed to solicit information regarding memory self-efficacy, memory management, memory remediation, and fears about memory aging in adulthood. Results indicated that (a) important dates, such as birthdays and anniversaries, were easily remembered, but names were not; (b) external memory aids were used most frequently; (c) a desire to improve memory for names and certain types of verbal information was expressed; and (d) loss of independence emerged as a fear associated with memory aging. Implications of these findings for the design of strategies to improve everyday memory performance and clinical memory management in older adults are discussed.     

Earwitness Testimony: Never Mind the Variety,Hear the Length

Three aspects of voice recognition were investigated in the study reported here: memory for familiar voices, memory for the words spoken, and the relative effects of length and variation in a voice extract on long- and short-term memory. In Experiment 1, recognition memory for the briefly heard voice of a stranger was superior with longer extracts (p<0.01), but increasing vowel variety did not improve performance. This pattern was repeated for short-term memory (p<0.01) in Experiment 2. Scores for the above task correlated significantly (p<0.05) with scores for recognizing well-known voices. In a further test of well-known voice memory in Experiment 3, a weak and non-significant positive correlation (r=0.29) was found between memory for well-known voices and memory for a once-heard voice. Memory for the words spoken did not correlate significantly with memory for the unknown voice itself. The possibilities of a memory-for-voices general ability, and forensic applications of the findings are discussed. © 1997 by John Wiley & Sons, Ltd.     

Ambiguity in pictorial depth

Pictorial space is the 3-D impression that one obtains when looking 'into' a 2-D picture. One is aware of 3-D 'opaque' objects. 'Pictorial reliefs' are the surfaces of such pictorial objects in 'pictorial space'. Photographs (or any pictures) do in no way fully specify physical scenes. Rather, any photograph is compatible with an infinite number of possible scenes that may be called 'metameric scenes'. If pictorial relief is one of these metameric scenes, the response may be considered 'veridical'. The conventional usage is more restrictive and is indeed inconsistent. Thus the observer has much freedom in arriving at such a 'veridical' response. To address this ambiguity, we determined the pictorial reliefs for eight observers, six pictures, and two psychophysical methods. We used 'methods of cross-sections' to operationalise pictorial reliefs. We find that linear regression of the depths of relief at corresponding locations in the picture for different observers often lead to very low (even insignificant) R2s. Thus the responses are idiosyncratic to a large degree. Perhaps surprisingly, we also observed that multiple regression of depth and picture coordinates at corresponding locations often lead to very high R2s. Often R2s increased from insignificant up to almost 1. Apparently, to a large extent 'depth' is irrelevant as a psychophysical variable, in the sense that it does not uniquely account for the relation of the response to the pictorial structure. This clearly runs counter to the bulk of the literature on pictorial 'depth perception'. The invariant core of interindividual perception proves to be of an 'affine' rather than a Euclidean nature; that is to say, 'pictorial space' is not simply the picture plane augmented with a depth dimension.     

Short-term memory for emotional faces in dysphoria

The study aimed to determine if the memory bias for negative faces previously demonstrated in depression and dysphoria generalises from long- to short-term memory. A total of 29 dysphoric (DP) and 22 non-dysphoric (ND) participants were presented with a series of faces and asked to identify the emotion portrayed (happiness, sadness, anger, or neutral affect). Following a delay, four faces were presented (the original plus three distractors) and participants were asked to identify the target face. Half of the trials assessed memory for facial emotion, and the remaining trials examined memory for facial identity. At encoding, no group differences were apparent. At memory testing, relative to ND participants, DP participants exhibited impaired memory for all types of facial emotion and for facial identity when the faces featured happiness, anger, or neutral affect, but not sadness. DP participants exhibited impaired identity memory for happy faces relative to angry, sad, and neutral, whereas ND participants exhibited enhanced facial identity memory when faces were angry. In general, memory for faces was not related to performance at encoding. However, in DP participants only, memory for sad faces was related to sadness recognition at encoding. The results suggest that the negative memory bias for faces in dysphoria does not generalise from long- to short-term memory.     

Feature-based attention resolves depth ambiguity

Perceiving the world around us requires that we resolve ambiguity. This process is often studied in the lab using ambiguous figures whose structures can be interpreted in multiple ways. One class of figures contains ambiguity in its depth relations, such that either of two surfaces could be seen as being the “front” of an object. Previous research suggests that selectively attending to a given location on such objects can bias the perception of that region as the front. This study asks whether selectively attending to a distributed feature can also bias that region toward the front. Participants viewed a structure-from-motion display of a rotating cylinder that could be perceived as rotating clockwise or counterclockwise (as imagined viewing from the top), depending on whether a set of red or green moving dots were seen as being in the front. A secondary task encouraged observers to globally attend to either red or green. Results from both Experiment 1 and 2 showed that the dots on the cylinder that shared the attended feature, and its corresponding surface, were more likely to be seen as being in the front, as measured by participants’ clockwise versus counterclockwise percept reports. Feature-based attention, like location-based attention, is capable of biasing competition among potential interpretations of figures with ambiguous structure in depth.     

Memory narrowing in children and adults

The memory narrowing effect posits that stress enhances memory for central information at the expense of memory for peripheral details. This effect is well established in adults, but not in children, although studies have not directly compared children's and adults' memory for central versus peripheral details of an identical distressing experience. In the present study, 9–12 year‐old and adult participants completed a laboratory stressor during which measures of self‐reported stress was collected. Two weeks later, participants returned for a surprise memory test regarding central and peripheral details of the laboratory stressor. Greater stress predicted memory narrowing in both children and adults, as indexed via decreased correct responses and increased don't know responses to questions about peripheral relative to central details. Findings have implications for theories concerning stress and memory, particularly in children, and for evaluating eyewitness memory in legal contexts. Copyright © 2010 John Wiley & Sons, Ltd.     

Compared to what? The effects of a frame of reference on older adults’ subjective memory

It is often unclear what comparisons older adults make when evaluating their own memory. If thinking about their memory relative to others, they may assess their own abilities differently than if comparing it to their past capabilities. To test the effect of reference frames on memory assessments and memory performance, we randomly assigned 120 older adults to one of three conditions in which we manipulated frames of reference (control, past-self comparison, or other adults comparison) on a memory self-efficacy questionnaire. Participants also completed general and specific memory predictions and an objective memory test. Participants in the past-self condition reported significantly lower global memory self-efficacy compared with the other adults and control conditions. No condition differences emerged for memory predictions, objective memory, or the likelihood of over- or underpredicting memory performance. These findings suggest that reference frames impact global memory self-efficacy, but do not influence the accuracy of subjective memory judgments.