Super-optimality and relative distance coding in location memory.

The prevailing model of landmark integration in location memory is Maximum Likelihood Estimation, which assumes that each landmark implies a target location distribution that is narrower for more reliable landmarks. This model assumes weighted linear combination of landmarks and predicts that, given optimal integration, the reliability with multiple landmarks is the sum of the reliabilities with the individual landmarks. Super-optimality is reliability with multiple landmarks exceeding optimal reliability given the reliability with each landmark alone; this is shown when performance exceeds predicted optimal performance, found by aggregating reliability values with single landmarks. Past studies claiming super-optimality have provided arguably impure measures of performance with single landmarks given that multiple landmarks were presented at study in conditions with a single landmark at test, disrupting encoding specificity and thereby leading to underestimation in predicted optimal performance. This study, unlike those prior studies, only presented a single landmark at study and the same landmark at test in single landmark trials, showing super-optimality conclusively. Given that super-optimal information integration occurs, emergent information, that is, information only available with multiple landmarks, must be used. With the target and landmarks all in a line, as throughout this study, relative distance is the only emergent information available. Use of relative distance was confirmed here by finding that, when both landmarks are left of the target at study, the target is remembered further right of its true location the further left the left landmark is moved from study to test.

Direction and distance information in memory for locations of objects relative to landmarks and boundaries.

An observer often remembers an object's location on the basis of its direction and distance from reference objects. Two kinds of reference object are of particular interest: landmarks and boundaries. We compared how well observers remembered the direction and distance of target objects from a landmark and a boundary. Patterns of variable error implied that the landmark was more effective than the boundary in supporting memory for target object direction. When the predictions of the landmark and the boundary were placed in conflict, patterns of constant error implied that the boundary was more effective than the landmark in supporting memory for target object distance. These results suggest affinities between direction information and landmarks and between distance information and boundaries. They raise the possibility that, rather than collapsing across direction and distance error, theoretical analyses should distinguish the two kinds of error in assessing the reliability of landmarks and boundaries.

Greater sensitivity in separation discrimination with closer spacing of separation levels tested.

We explored the effects of spacing in the levels of separation tested in a separation discrimination task. Participants indicated, for pairs of test circles, whether the separation between them was greater than a standard separation. A critical set of equally-spaced separation levels was tested in two conditions. In one condition additional separation levels were interleaved between the critical levels. In the other condition additional separation levels were not interleaved. Overall, the same average level and range of levels were tested in the two conditions, and the levels tested were equally spaced in both conditions. Critically, the levels tested were more closely spaced in one condition than the other. The sensitivity of the discrimination was greater in the condition with the more as opposed to less-closely spaced levels of separation. We suggest an explanation under which separation is assessed from the number of "separation fields" between the points at which the test stimuli register and under which the separation fields are smaller or more densely distributed when the levels of separation tested are more as opposed to less-closely spaced.

Errors of Analysis in Distance Assessment: Effects of Vertical on Horizontal Components.

(a) Participants indicated, for pairs of circles whose locations varied on the horizontal and vertical axes of a frontal plane, whether the horizontal distance between the circles exceeded a target horizontal distance. The error rate depended on the vertical as well as the horizontal distance between the circles. (b) Participants indicated, for pairs of circles that were varying horizontal (or vertical) distances and a constant vertical (or horizontal) distance apart in a frontal plane, whether the horizontal (or vertical) distance between them matched a target horizontal (or vertical) distance. Incorrect "match" responses were more likely if the horizontal (or vertical) distance between the circles was less than as opposed to greater than the target distance. The results suggest that distance judgments for pairs of stimuli varying on the horizontal and vertical axes are based on the overall distance between the stimuli, with the relevant axis given more weight than the irrelevant axis in assessment of the distance. The results do not support the view that that such distance judgments are based on the relevant distance between the stimuli, with the relevant and irrelevant axes being erroneously interchanged on some iterations of the assessment process.

Horizontal-vertical anisotropy with respect to bias and sensitivity.

Previous research suggests that participants are biased to assess horizontal distances as smaller than vertical distances. We explored the effect of horizontal versus vertical orientation on the sensitivity, as well as the bias, of distance judgments. In contrast to participants of most past studies, our participants never directly compared horizontal and vertical distances. On each trial, participants judged the horizontal or vertical distance between a pair of horizontally or vertically oriented dots as being greater than or less than the average distance between previously presented pairs of dots of the same orientation. When the same participants judged horizontal and vertical distance, the distance judged greater than average 50% of the time (P50) was larger for horizontal than for vertical judgments-a pattern consistent with the horizontal-vertical bias of past work. When different participants judged horizontal and vertical distance, the horizontal and vertical P50s did not differ. When participants did not know whether they would judge horizontal or vertical distance on the coming trial, sensitivity was lower for horizontal than vertical judgments. When participants knew what kind of judgment they would make on the coming trial, sensitivity did not differ for horizontal and vertical judgments. We consider the implications of these findings for accounts that attribute the horizontal-vertical bias (1) to real-world-retinal mapping, (2) to the elliptical shape of the visual field, or (3) to the asymmetry of the receptive fields used to assess frontal distance. We suggest that distance field asymmetry must be invoked to explain the present sensitivity effect.

Getting completely turned around: how disorientation impacts subjective straight ahead.

In manipulating a pointer to indicate subjective straight ahead (SSA), participants were more variable after a series of whole-body rotations in conjunction with external sensory blockade than after external sensory blockade alone. The variability of reported SSA did not increase consequent to a temporal delay matched to the time taken by the rotation procedure. These results suggest that an observer's egocentric reference frame is more complex and less stable than has previously been thought.

How is visual separation assessed? By counting distance units.

How does the human visual system assess the separation between pairs of stimuli in a frontal plane? According to the direct (or subtractive) view the system finds the difference between the positions of the stimuli in a localization system. According to the indirect (or additive) view the system finds the number of instances of a distance unit lying between representations of the stimuli. Critically, position is explicitly represented under the direct view, with separation being derived from position. Position is not explicitly represented under the indirect view; separation is consequently inferred by counting an internal unit of distance. Recent results favor the indirect over the direct view of separation assessment. Dissociations between assessments of separation and position, various context effects in the assessment of separation, and suggestions that position information is not cleanly accessed argue against the direct view. At the same time, various context effects in separation assessment argue for the indirect view. Recent findings regarding the brain bases of vision are consistent with the indirect view. In short, recent results suggest that assessing the separation between two frontal stimuli involves integrating distance units between representations of the stimuli.

Two-category place representations persist over body rotations.

We explored a system that constructs environment-centered frames of reference and coordinates memory for the azimuth of an object in an enclosed space. For one group, we provided two environmental cues (doors): one in the front, and one in the rear. For a second group, we provided two object cues: a front and a rear cue. For a third group, we provided no external cues; we assumed that for this group, their reference frames would be determined by the orthogonal geometry of the floor-and-wall junction that divides a space in half or into multiple territories along the horizontal continuum. Using Huttenlocher, Hedges, and Duncan's (Psychological Review 98: 352-376, 1991) category-adjustment model (cue-based fuzzy boundary version) to fit the data, we observed different reference frames than have been seen in prior studies involving two-dimensional domains. The geometry of the environment affected all three conditions and biased the remembered object locations within a two-category (left vs. right) environmental frame. The influence of the environmental geometry remained observable even after the participants' heading within the environment changed due to a body rotation, attenuating the effect of the front but not of the rear cue. The door and object cues both appeared to define boundaries of spatial categories when they were used for reorientation. This supports the idea that both types of cues can assist in environment-centered memory formation.

Direction and distance information in memory for location relative to landmarks.

An object's location is often remembered relative to one or more landmarks. An object has a certain direction and distance relative to a landmark. When multiple landmarks are available the information from the different landmarks is integrated. In the prevailing view direction and distance are equally influential in the integration process. We present evidence that direction and distance are not always equally influential in landmark-based memory. During the study phase of our task, participants viewed a set of layouts, each comprising a target and two landmarks. During the test phase participants attempted to place each target in the correct location relative to the two landmarks. Our measure of direction deviation indexed the degree to which the targets were placed on the basis of distance rather than solely on the basis of direction. Our measure of distance deviation indexed the degree to which the targets were placed on the basis of direction rather than solely on the basis of distance. Direction deviation was smaller than distance deviation. The results suggest that direction is more influential than distance in memory for the locations of objects relative to landmarks.

The bias for a recognition judgement depends on the response emitted in a prior recognition judgement.

On each trial of the experimental procedure the participant read a list of words and made successive recognition judgements to multiple test words. The bias for a given recognition judgement was more conservative if the judgement followed a correct positive response to a target than if it followed a correct negative response to a lure. Similar results were not observed for successive semantic recognition judgements. The bias shift was greater when the study list was short than when the list was long. The results suggest that participants in a recognition task have a sense of the size of the set of targets that might possibly be presented on the next trial and that, under conditions in which a word can only be presented once during the test phase, their bias becomes more conservative after a positive response to a target because the set is depleted.

Probability of target recollection varies with target-lure relatedness under the dual process signal detection model.

The ROC function plots hit and false alarm rates against one another. For item recognition the z-transformed ROC (Z-ROC) function is typically linear with slope less than one. The Dual Process Signal Detection (DPSD) and Unequal Variance Signal Detection (UVSD) models see the slope as reflecting the ratio of the lure and target evidence standard deviations. The DPSD model in addition sees the slope as co-varying with estimates of target recollection probability (R). This follows because the slope decreases with increases in the target evidence standard deviation which in turn increases with increases in the numbers of high evidence recollection items. However our results suggest that the lure evidence standard deviation, and thus the Z-ROC slope, can vary with factors seemingly unrelated to target recollection, posing problems for DPSD estimates of R. In word recognition the standard deviation of lure confidence ratings and the slope of the z-ROC function were larger with semantically related than unrelated lures. When the data for related and unrelated lures were fit separately, the standard two-parameter DPSD model, implausibly, set R lower for related than unrelated lures. The UVSD model, more plausibly, set the lure evidence standard deviation larger for related than unrelated lures.

Spatial memory during progressive disorientation.

Human spatial representations of object locations in a room-sized environment were probed for evidence that the object locations were encoded relative not just to the observer (egocentrically) but also to each other (allocentrically). Participants learned the locations of 4 objects and then were blindfolded and either (a) underwent a succession of 70 degrees and 200 degrees whole-body rotations or (b) were fully disoriented and then underwent a similar sequence of 70 degrees and 200 degrees rotations. After each rotation, participants pointed to the objects without vision. Analyses of the pointing errors suggest that as participants lost orientation, represented object directions generally "drifted" off of their true directions as an ensemble, not in random, unrelated directions. This is interpreted as evidence that object-to-object (allocentric) relationships play a large part in the human spatial updating system. However, there was also some evidence that represented object directions occasionally drifted off of their true directions independently of one another, suggesting a lack of allocentric influence. Implications regarding the interplay of egocentric and allocentric information are considered.

Misperception of exocentric directions in auditory space.

Previous studies have demonstrated large errors (over 30 degrees ) in visually perceived exocentric directions (the direction between two objects that are both displaced from the observer's location; e.g., Philbeck et al. [Philbeck, J. W., Sargent, J., Arthur, J. C., & Dopkins, S. (2008). Large manual pointing errors, but accurate verbal reports, for indications of target azimuth. Perception, 37, 511-534]). Here, we investigated whether a similar pattern occurs in auditory space. Blindfolded participants either attempted to aim a pointer at auditory targets (an exocentric task) or gave a verbal estimate of the egocentric target azimuth. Targets were located at 20-160 degrees azimuth in the right hemispace. For comparison, we also collected pointing and verbal judgments for visual targets. We found that exocentric pointing responses exhibited sizeable undershooting errors, for both auditory and visual targets, that tended to become more strongly negative as azimuth increased (up to -19 degrees for visual targets at 160 degrees ). Verbal estimates of the auditory and visual target azimuths, however, showed a dramatically different pattern, with relatively small overestimations of azimuths in the rear hemispace. At least some of the differences between verbal and pointing responses appear to be due to the frames of reference underlying the responses; when participants used the pointer to reproduce the egocentric target azimuth rather than the exocentric target direction relative to the pointer, the pattern of pointing errors more closely resembled that seen in verbal reports. These results show that there are similar distortions in perceiving exocentric directions in visual and auditory space.

Measuring cognitive distance in the network representations of texts.

Pairs of words are identified more quickly as coming from different sentences the further apart the words are in the network representation of their native text. How is the distance between the words measured? According to the network connection hypothesis, the distance between 2 words is the length of the network path between the propositions to which they belong, as measured by a process of spreading activation. According to the location code hypothesis, the distance between 2 words is the difference between codes that record the locations of their propositions in the network representation. The results of 3 experiments supported the network connection hypothesis.

Analytic processing of distance.

How does a human observer extract from the distance between two frontal points the component corresponding to an axis of a rectangular reference frame? To find out we had participants classify pairs of small circles, varying on the horizontal and vertical axes of a computer screen, in terms of the horizontal distance between them. A response signal controlled response time. The error rate depended on the irrelevant vertical as well as the relevant horizontal distance between the test circles with the relevant distance effect being larger than the irrelevant distance effect. The results implied that the horizontal distance between the test circles was imperfectly extracted from the overall distance between them. The results supported an account, derived from the Exemplar Based Random Walk model (Nosofsky & Palmieri, 1997), under which distance classification is based on the overall distance between the test circles, with relevant distance being extracted from overall distance to the extent that the relevant and irrelevant axes are differentially weighted so as to reduce the contribution of irrelevant distance to overall distance. The results did not support an account, derived from the General Recognition Theory (Ashby & Maddox, 1994), under which distance classification is based on the relevant distance between the test circles, with the irrelevant distance effect arising because a test circle's perceived location on the relevant axis depends on its location on the irrelevant axis, and with relevant distance being extracted from overall distance to the extent that this dependency is absent.

Variation in the standard deviation of the lure rating distribution: Implications for estimates of recollection probability.

In word recognition semantic priming of test words increased the false-alarm rate and the mean of confidence ratings to lures. Such priming also increased the standard deviation of confidence ratings to lures and the slope of the z-ROC function, suggesting that the priming increased the standard deviation of the lure evidence distribution. The Unequal Variance Signal Detection (UVSD) model interpreted the priming as increasing the standard deviation of the lure evidence distribution. Without additional parameters the Dual Process Signal Detection (DPSD) model could only accommodate the results by fitting the data for related and unrelated primes separately, interpreting the priming, implausibly, as decreasing the probability of target recollection (DPSD). With an additional parameter, for the probability of false (lure) recollection the model could fit the data for related and unrelated primes together, interpreting the priming as increasing the probability of false recollection. These results suggest that DPSD estimates of target recollection probability will decrease with increases in the lure confidence/evidence standard deviation unless a parameter is included for false recollection. Unfortunately the size of a given lure confidence/evidence standard deviation relative to other possible lure confidence/evidence standard deviations is often unspecified by context. Hence the model often has no way of estimating false recollection probability and thereby correcting its estimates of target recollection probability.

Aging and the Effects of Exploratory Behavior on Spatial Memory.

The present research examined the effect of encoding from multiple viewpoints on scene recall in a group of younger (18-22 years) and older (65-80 years) adults. Participants completed a visual search task, during which they were given the opportunity to examine a room using two sets of windows that partitioned the room differently. Their choice of window set was recorded, to determine whether an association between these choices and spatial memory performance existed. Subsequently, participants were tested for spatial memory of the domain in which the search task was completed. Relative to younger adults, older adults demonstrated an increased tendency to use a single set of windows as well as decreased spatial memory for the domain. Window-set usage was associated with spatial memory, such that older adults who relied more heavily on a single set of windows also had better performance on the spatial memory task. These findings suggest that, in older adults, moderation in exploratory behavior may have a positive effect on memory for the domain of exploration.

Dimensional interaction in distance judgment.

Participants decided under speed stress whether or not the horizontal distances between pairs of frontal locations exceeded a criterion distance. The error rate reflected parallel effects of the horizontal and vertical distance between the locations. Whereas dimensional interaction in perceptual judgment has previously been attributed either to the perception of the stimulus or to the response decision concerning the stimulus, here dimensional interaction was attributed to the process of distance assessment regarding the test locations. Under the proposed account, the horizontal distance between the locations could not be assessed independently of the vertical distance. Only the overall distance between the locations could be assessed. However, because the horizontal and vertical positions of the locations could be independently assessed, the horizontal distance between the locations was available to the extent that the vertical positions of the locations were weighted so as to minimize vertical distance prior to the assessment of overall distance. In support of this account, parallel effects of horizontal and vertical distance were not observed when participants decided whether or not pairs of locations had the same horizontal position.

Loss of distinctive features and a broader pattern of priming in Alzheimer's disease.

The results of 2 experiments support the contention that patients with Alzheimer's disease (AD) show a relative loss of the semantic features that distinguish concepts from one another and that the representations of pairs of concepts consequently share a larger proportion of their associated features in AD than in normal aging. In Experiment 1, AD patients listed fewer features for a set of concepts than did healthy older adults and were more deficient at listing features if the features were distinctive to particular concepts than if they were shared by multiple concepts. In Experiment 2, AD patients showed online priming at levels of relatedness at which healthy older adults did not.