Perceived spatial presence and body orientation affect the recall of out-of-sight places in an immersive sketching experiment.

The orientation of sketch maps of remote but familiar city squares produced from memory has been shown to depend on the distance and airline direction from the production site to the remembered square (position-dependent recall, Röhrich et al. in PLoS One 9(11): e112793, 2014). Here, we present a virtual reality version of the original experiment and additionally study the role of body orientation. Three main points can be made: First, "immersive sketching" is a novel and useful paradigm in which subjects sketch maps live on paper while being immersed in virtual reality. Second, the original effect of position-dependent recall was confirmed, indicating that the sense of being present at a particular location, even if generated in a virtual environment, suffices to bias the imagery of distant places. Finally, the orientation of the produced sketch maps depended also on the body orientation of the subjects. At each production site, body orientation was controlled by varying the position of the live feed in the virtual environment, such that subjects had to turn towards the prescribed direction. Position-dependent recall is strongest if subjects are aligned with the airline direction to the target and virtually goes away if they turn in the opposite direction. We conclude that the representation of out-of-sight target places depends on both the current airline direction to the target and the body orientation.

Metric information in cognitive maps: Euclidean embedding of non-Euclidean environments.

The structure of the internal representation of surrounding space, the so-called cognitive map, has long been debated. A Euclidean metric map is the most straight-forward hypothesis, but human navigation has been shown to systematically deviate from the Euclidean ground truth. Vector navigation based on non-metric models can better explain the observed behavior, but also discards useful geometric properties such as fast shortcut estimation and cue integration. Here, we propose another alternative, a Euclidean metric map that is systematically distorted to account for the observed behavior. The map is found by embedding the non-metric model, a labeled graph, into 2D Euclidean coordinates. We compared these two models using data from a human behavioral study where participants had to learn and navigate a non-Euclidean maze (i.e., with wormholes) and perform direct shortcuts between different locations. Even though the Euclidean embedding cannot correctly represent the non-Euclidean environment, both models predicted the data equally well. We argue that the embedding naturally arises from integrating the local position information into a metric framework, which makes the model more powerful and robust than the non-metric alternative. It may therefore be a better model for the human cognitive map.

Gateway identity and spatial remapping in a combined grid and place cell attractor.

The spatial specificities of hippocampal place cells, i.e., their firing fields, are subject to change if the rat enters a new compartment in the experimental maze. This effect is known as remapping. It cannot be explained from path integration (grid cell activity) and local sensory cues alone but requires additional knowledge of the different compartments in the form of context recognition at the gateways between them. Here we present a model for the hippocampal-entorhinal interplay in which the activity of place and grid cells follows a joint attractor dynamic. Place cells depend on the current grid cell activity but can also reset the grid cell activity in the remapping process. Remapping is triggered by the passage through a gateway. When this happens, a previously stored pattern of place cell activity associated with the gateway is reactivated from a "gateway database". The joint attractor will then reinstate the grid cell pattern that was active when the gateway had first been learned and path integration can proceed from there. The model is tested with various mazes used in the experimental literature and reproduces the published results, and we make predictions for remapping in a new maze type. We propose the involvement of memory in the form of "gate cells" that drive the place cells and with them the joint hippocampal-entorhinal loop into the corresponding attractor whenever a compartment is entered.

Response time and response time variability as indicators of response quality during static automated perimetry.

PURPOSE: Perimetry is a both demanding and strenuous examination method that is often accompanied by signs of fatigue, leading to false responses and thus incorrect results. Therefore, it is essential to monitor the response quality. The purpose of this study was to evaluate the response time (RT) and its variability (RTV) as quality indicators during static automated perimetry. METHODS: Size III Goldmann stimuli (25.7') were shown with the OCTOPUS 900 perimeter in four visual field locations with 13 different stimulus luminance levels (0.04-160 cd/m2). An increased rate of false-positive and false-negative catch trials (25% each) served to monitor the response quality simultaneously together with response time recording. Data evaluation was divided into global and individual analysis. For global analysis, the agreement indices (AI, agreement between time periods with an increased number of false responses to catch trials and time periods with pathological response to time-based values set into relation to time periods in which only one of the two criteria was considered pathological) and for individual analysis, the Spearman correlation coefficients were calculated. Ophthalmologically normal subjects with a visual acuity ≥ 0.8, and a maximum spherical/cylindrical ametropia of ± 8.00/2.50 dpt were included. RESULTS: Forty-eight subjects (18 males, 30 females, age 22-78 years) were examined. The total number of false responses to catch trials was (median/maximum): 6/82. RT and RTV were compared to the occurrence of incorrect responses to catch trials. The resulting individual Spearman correlation coefficients (median/maximum) were for RT: ρRT = 0.05/0.35 and for RTV: ρRTV = 0.27/0.61. The global analysis of the RTV showed agreement indices (median/maximum) of AIRTV = 0.14/0.47. CONCLUSIONS: According to this study, an increased portion of catch trials is suitable as a verification tool for possible response quality indicators. The RTV is a promising parameter for indicating the response quality.

Exploitation of image statistics with sparse coding in the case of stereo vision.

The sparse coding algorithm has served as a model for early processing in mammalian vision. It has been assumed that the brain uses sparse coding to exploit statistical properties of the sensory stream. We hypothesize that sparse coding discovers patterns from the data set, which can be used to estimate a set of stimulus parameters by simple readout. In this study, we chose a model of stereo vision to test our hypothesis. We used the Locally Competitive Algorithm (LCA), followed by a naïve Bayes classifier, to infer stereo disparity. From the results we report three observations. First, disparity inference was successful with this naturalistic processing pipeline. Second, an expanded, highly redundant representation is required to robustly identify the input patterns. Third, the inference error can be predicted from the number of active coefficients in the LCA representation. We conclude that sparse coding can generate a suitable general representation for subsequent inference tasks.

Place recognition from distant landmarks: human performance and maximum likelihood model.

We present a simple behavioral experiment on human place recognition from a configuration of four visual landmarks. Participants were asked to navigate several paths, all involving a turn at one specific point, and while doing so incidentally learned the position of that turning point. In the test phase, they were asked to return to the turning point in a reduced environment leaving only the four landmarks visible. Results are compared to two versions of a maximum likelihood model of place recognition using either view-based or depth-based cues for place recognition. Only the depth-based model is in good qualitative agreement with the data. In particular, it reproduces landmark configuration-dependent effects of systematic bias and statistical error distribution as well as effects of approach direction. The model is based on a place code (depth and bearing of the landmarks at target location) and an egocentric working memory of surrounding space including current landmark position in a local, map-like representation. We argue that these elements are crucial for human place recognition.

Naturalistic path integration of Cataglyphis desert ants on an air-cushioned lightweight spherical treadmill.

Air-cushioned spheres are widely used as treadmills to study behavioural and neurophysiological questions in numerous species. We describe an improved spherical treadmill design that reliably registers the path and walking behaviour of an animal walking on top of the sphere. The simple and robust set-up consists of a very light hollowed styrofoam ball supported by an air stream in a hollow half sphere and can be used indoors and outdoors. Two optical mouse sensors provided with lenses of 4.6 mm focal length detect the motion of the sphere with a temporal resolution of more than 200 frames s-1 and a spatial resolution of less than 0.2 mm. The treadmill can be used in an open- or closed-loop configuration with respect to yaw of the animal. The tethering allows animals to freely adjust their body posture and in the closed-loop configuration to quickly rotate around their yaw axis with their own moment of inertia. In this account, we present the first evidence of naturalistic homing navigation on a spherical treadmill for two species of Cataglyphis desert ants. We were able to evaluate with good precision the walking speed and angular orientation at any time. During homing the ants showed a significant difference in walking speed between the approach and search phases; moreover, they slowed down significantly as soon as they reached zero vector state, the fictive nest position.

The perception of ego-motion change in environments with varying depth: Interaction of stereo and optic flow.

When estimating ego-motion in environments (e.g., tunnels, streets) with varying depth, human subjects confuse ego-acceleration with environment narrowing and ego-deceleration with environment widening. Festl, Recktenwald, Yuan, and Mallot (2012) demonstrated that in nonstereoscopic viewing conditions, this happens despite the fact that retinal measurements of acceleration rate-a variable related to tau-dot-should allow veridical perception. Here we address the question of whether additional depth cues (specifically binocular stereo, object occlusion, or constant average object size) help break the confusion between narrowing and acceleration. Using a forced-choice paradigm, the confusion is shown to persist even if unambiguous stereo information is provided. The confusion can also be demonstrated in an adjustment task in which subjects were asked to keep a constant speed in a tunnel with varying diameter: Subjects increased speed in widening sections and decreased speed in narrowing sections even though stereoscopic depth information was provided. If object-based depth information (stereo, occlusion, constant average object size) is added, the confusion between narrowing and acceleration still remains but may be slightly reduced. All experiments are consistent with a simple matched filter algorithm for ego-motion detection, neglecting both parallactic and stereoscopic depth information, but leave open the possibility of cue combination at a later stage.

How to Best Name a Place? Facilitation and Inhibition of Route Learning Due to Descriptive and Arbitrary Location Labels.

Establishing verbal memory traces for non-verbal stimuli was reported to facilitate or inhibit memory for the non-verbal stimuli. We show that these effects are also observed in a domain not indicated before-wayfinding. Fifty-three participants followed a guided route in a virtual environment. They were asked to remember half of the intersections by relying on the visual impression only. At the other 50% of the intersections, participants additionally heard a place name, which they were asked to memorize. For testing, participants were teleported to the intersections and were asked to indicate the subsequent direction of the learned route. In Experiment 1, intersections' names were arbitrary (i.e., not related to the visual impression). Here, participants performed more accurately at unnamed intersections. In Experiment 2, intersections' names were descriptive and participants' route memory was more accurate at named intersections. Results have implications for naming places in a city and for wayfinding aids.

Modality dependence and intermodal transfer in the Corsi Spatial Sequence Task: Screen vs. Floor.

Four versions of the Corsi Spatial Sequence Task (CSST) were tested in a complete within-subject design, investigating whether participants' performance depends on the modality of task presentation and reproduction that put different demands on spatial processing. Presentation of the sequence (encoding phase) and the reproduction (recall phase) were each carried out either on a computer screen or on the floor of a room, involving actual walking in the recall phase. Combinations of the two different encoding and recall procedures result in the modality conditions Screen-Screen, Screen-Floor, Floor-Screen, and Floor-Floor. Results show the expected decrease in performance with increasing sequence length, which is likely due to processing limitations of working memory. We also found differences in performance between the modality conditions indicating different involvements of spatial working memory processes. Participants performed best in the Screen-Screen modality condition. Floor-Screen and Floor-Floor modality conditions require additional working memory resources for reference frame transformation and spatial updating, respectively; the resulting impairment of the performance was about the same in these two conditions. Finally, the Screen-Floor modality condition requires both types of additional spatial demands and led to the poorest performance. Therefore, we suggest that besides the well-known spatial requirements of CSST, additional working memory resources are demanded in walking CSST supporting processes such as spatial updating, mental rotation, reference frame transformation, and the control of walking itself.

How to construct a linguistic landmark: language cues in the formation of hierarchical representations of space.

The formation of a hierarchical representation of space can be induced by the spatial adjacency of places marked by landmark objects from the same semantic category, as was demonstrated by a route-planning experiment (Wiener and Mallot in Spat Cogn Comput 3(4):331-358, 2003). Using the same paradigm, we tested the efficiency of linguistic cues with various hierarchical categorization principles in regional structuring. In five different conditions, places of the experimental environment were characterized (1) by landmark objects, (2) by arbitrary proper names on region level, (3) by prototypical names on region level, (4) by nouns from different semantic categories, and (5) by groups of nouns with intrinsic whole-part relation. A region effect comparable to the landmark object condition was found only for the whole-part relations, which combine spatial proximity with a shared context. A linguistic analysis revealed a correspondence to the intended regional subdivision only for the cues of this condition.

An artificial elementary eye with optic flow detection and compositional properties.

We describe a 2 mg artificial elementary eye whose structure and functionality is inspired by compound eye ommatidia. Its optical sensitivity and electronic architecture are sufficient to generate the required signals for the measurement of local optic flow vectors in multiple directions. Multiple elementary eyes can be assembled to create a compound vision system of desired shape and curvature spanning large fields of view. The system configurability is validated with the fabrication of a flexible linear array of artificial elementary eyes capable of extracting optic flow over multiple visual directions.

Allocation of cognitive resources in comparative visual search--individual and task dependent effects.

Behaviors recruit multiple, mutually substitutable types of cognitive resources (e.g., data acquisition and memorization in comparative visual search), and the allocation of resources is performed in a cost-optimizing way. If costs associated with each type of resource are manipulated, e.g., by varying the complexity of the items studied or the visual separation of the arrays to be compared, according adjustments of resource allocation ("trade-offs") have been demonstrated. Using between-subject designs, previous studies showed overall trade-off behavior but neglected inter-individual variability of trade-off behavior. Here, we present a simplified paradigm for comparative visual search in which gaze-measurements are replaced by switching of a visual mask covering one stimulus array at a time. This paradigm allows for a full within-subject design. While overall trade-off curves could be reproduced, we found that each subject used a specific trade-off strategy which differ substantially between subjects. Still, task-dependent adjustment of resource allocation can be demonstrated but accounts only for a minor part of the overall trade-off range. In addition, we show that the individual trade-offs were adjusted in an unconscious and rather intuitive way, enabling a robust manifestation of the selected strategy space.

View-based organization and interplay of spatial working and long-term memories.

Space perception provides egocentric, oriented views of the environment from which working and long-term memories are constructed. "Allocentric" (i.e. position-independent) long-term memories may be organized as graphs of recognized places or views but the interaction of such cognitive graphs with egocentric working memories is unclear. Here we present a simple coherent model of view-based working and long-term memories, together with supporting evidence from behavioral experiments. The model predicts (i) that within a given place, memories for some views may be more salient than others, (ii) that imagery of a target square should depend on the location where the recall takes place, and (iii) that recall favors views of the target square that would be obtained when approaching it from the current recall location. In two separate experiments in an outdoor urban environment, pedestrians were approached at various interview locations and asked to draw sketch maps of one of two well-known squares. Orientations of the sketch map productions depended significantly on distance and direction of the interview location from the target square, i.e. different views were recalled at different locations. Further analysis showed that location-dependent recall is related to the respective approach direction when imagining a walk from the interview location to the target square. The results are consistent with a view-based model of spatial long-term and working memories and their interplay.

Odometry for ground moving agents by optic flow recorded with optical mouse chips.

Optical mouse chips-equipped with adequate lenses-can serve as small, light, precise, fast, and cheap motion sensors monitoring optic flow induced by self motion of an agent in a contrasted environment. We present a device that extracts self motion parameters exclusively from flow in eight mouse sensors. Four pairs of sensors with opposite azimuth are mounted on a sensor head, each individual sensor looking down with -45° elevation. The head is mounted on a carriage and is moved at constant height above a textured planar ground. The calibration procedure and tests on the precision of self motion estimates are reported.

Gaze movements and spatial working memory in collision avoidance: a traffic intersection task.

Street crossing under traffic is an everyday activity including collision detection as well as avoidance of objects in the path of motion. Such tasks demand extraction and representation of spatio-temporal information about relevant obstacles in an optimized format. Relevant task information is extracted visually by the use of gaze movements and represented in spatial working memory. In a virtual reality traffic intersection task, subjects are confronted with a two-lane intersection where cars are appearing with different frequencies, corresponding to high and low traffic densities. Under free observation and exploration of the scenery (using unrestricted eye and head movements) the overall task for the subjects was to predict the potential-of-collision (POC) of the cars or to adjust an adequate driving speed in order to cross the intersection without collision (i.e., to find the free space for crossing). In a series of experiments, gaze movement parameters, task performance, and the representation of car positions within working memory at distinct time points were assessed in normal subjects as well as in neurological patients suffering from homonymous hemianopia. In the following, we review the findings of these experiments together with other studies and provide a new perspective of the role of gaze behavior and spatial memory in collision detection and avoidance, focusing on the following questions: (1) which sensory variables can be identified supporting adequate collision detection? (2) How do gaze movements and working memory contribute to collision avoidance when multiple moving objects are present and (3) how do they correlate with task performance? (4) How do patients with homonymous visual field defects (HVFDs) use gaze movements and working memory to compensate for visual field loss? In conclusion, we extend the theory of collision detection and avoidance in the case of multiple moving objects and provide a new perspective on the combined operation of external (bottom-up) and internal (top-down) cues in a traffic intersection task.

Miniature curved artificial compound eyes.

In most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories.

Detection of linear ego-acceleration from optic flow.

Human observers are able to estimate various ego-motion parameters from optic flow, including rotation, translational heading, time-to-collision (TTC), time-to-passage (TTP), etc. The perception of linear ego-acceleration or deceleration, i.e., changes of translational velocity, is less well understood. While time-to-passage experiments indicate that ego-acceleration is neglected, subjects are able to keep their (perceived) speed constant under changing conditions, indicating that some sense of ego-acceleration or velocity change must be present. In this paper, we analyze the relation of ego-acceleration estimates and geometrical parameters of the environment using simulated flights through cylindrical and conic (narrowing or widening) corridors. Theoretical analysis shows that a logarithmic ego-acceleration parameter, called the acceleration rate ρ, can be calculated from retinal acceleration measurements. This parameter is independent of the geometrical layout of the scene; if veridical ego-motion is known at some instant in time, acceleration rate allows updating of ego-motion without further depth-velocity calibration. Results indicate, however, that subjects systematically confuse ego-acceleration with corridor narrowing and ego-deceleration with corridor widening, while veridically judging ego-acceleration in straight corridors. We conclude that judgments of ego-acceleration are based on first-order retinal flow and do not make use of acceleration rate or retinal acceleration.

Gaze patterns predicting successful collision avoidance in patients with homonymous visual field defects.

Aim of the present study was to identify efficient compensatory gaze patterns applied by patients with homonymous visual field defects (HVFDs) under virtual reality (VR) conditions in a dynamic collision avoidance task. Thirty patients with HVFDs due to vascular brain lesions and 30 normal subjects performed a collision avoidance task with moving objects at an intersection under two difficulty levels. Based on their performance (i.e. the number of collisions), patients were assigned to either an "adequate" (HVFD(A)) or "inadequate" (HVFD(I)) subgroup by the median split method. Eye and head tracking data were available for 14 patients and 19 normal subjects. Saccades, fixations, mean number of gaze shifts, scanpath length and the mean gaze eccentricity, were compared between HVFD(A), HVFD(I) patients and normal subjects. For both difficulty levels, the gaze patterns of HVFD(A) patients (N=5) compared to HVFD(I) patients (N=9) were characterized by longer saccadic amplitudes towards both the affected and the intact side, larger mean gaze eccentricity, more gaze shifts, longer scanpaths and more fixations on vehicles but fewer fixations on the intersection. Both patient groups displayed more fixations in the affected compared to the intact hemifield. Fixation number, fixation duration, scanpath length, and number of gaze shifts were similar between HVFD(A) patients and normal subjects. Patients with HVFDs who adapt successfully to their visual deficit, display distinct gaze patterns characterized by increased exploratory eye and head movements, particularly towards moving objects of interest on their blind side. In the context of a dynamic environment, efficient compensation in patients with HVFDs is possible by means of gaze scanning. This strategy allows continuous update of the moving objects' spatial location and selection of the task-relevant ones, which will be represented in visual working memory.

The neural correlates of impaired collision avoidance in hemianopic patients.

PURPOSE: The aim of this study was to assess the brain regions associated with impaired performance in a virtual, dynamic collision avoidance task, in a group of patients with homonymous visual field defects (HVFDs) because of unilateral vascular brain lesions. METHODS: Overall task performance was quantitatively assessed as the number of collisions while crossing an intersection at two levels of traffic density. Twenty-six patients were divided into two subgroups using the median split method: patients with 'performance above average' (HVFD(A), i.e. lower number of collisions) and patients with 'performance below average' (HVFD(B), i.e. higher number of collisions). In order to identify the anatomical structures that might be specifically affected in HVFD(B) patients but spared in HVFD(A) patients, overlap, subtraction and voxel-based lesion-symptom mapping analyses were performed using the MRIcron software. RESULTS: No significant difference in collision avoidance between patients with left- and right-hemispheric lesions was revealed. Separate lesion analysis in 12 patients with right- and 14 patients with left-hemispheric lesions showed that the cortical structures associated with impaired collision avoidance were the parieto-occipital region and posterior cingulate gyrus in the right hemisphere and the inferior occipital cortex and parts of the fusiform (occipito-temporal) gyrus in the left hemisphere. CONCLUSION: In the present collision avoidance paradigm, impaired performance of patients with right-hemispheric lesions is associated with damage in the dorsal processing stream and potential impact on the visual spatial working memory (WM), while impaired performance of patients with left-hemispheric lesions is associated with damage in the ventral stream and potential impact on the visual object WM.