Dissociation between perception and smooth pursuit eye movements in speed judgments of moving Gabor targets.

The relationship between eye movements and subjective perception is still relatively poorly understood. In this study, participants tracked the movement of a Gabor patch and made perceptual judgments of its speed using a two-interval forced choice task. The Gabor patch could either have a static carrier or a carrier moving in the same or opposite direction as the overall envelope motion. We found that smooth pursuit speed was strongly affected by the internal motion of the Gabor carrier, with faster smooth pursuit being made to targets with internal motion in the same direction as overall motion compared to targets with internal motion in the opposite direction. However, we found that there were only small and highly variable differences in the perceptual speed judgments made simultaneously, and that these perceptual and smooth pursuit measures did not significantly correlate with each other. This contrasts with the number of catch-up saccades (saccades made in the direction of overall target motion), which was significantly correlated with the simultaneous perceptual judgments. There was also a significant correlation between perceptual judgments and the difference between the target and eye position immediately before a saccade. These results suggest that it is possible to see dissociations between vision and action in this task, and that the specific type of visual action studied may determine the relationship with perception

A Bayesian statistical model is able to predict target-by-target selection behaviour in a human foraging task

Funding: This research was funded by the Economic and Social Research Council grant number ES/S016120/1 to A.D.F.C and A.R.H. Acknowledgments: The authors would like to thank all the researchers who publicly shared their data.Peer reviewedPostprintPublisher PD

The role of stripe orientation in target capture success.

INTRODUCTION: 'Motion dazzle' refers to the hypothesis that high contrast patterns such as stripes and zigzags may have evolved in a wide range of animals as they make it difficult to judge the trajectory of an animal in motion. Despite recent research into this idea, it is still unclear to what extent stripes interfere with motion judgement and if effects are seen, what visual processes might underlie them. We use human participants performing a touch screen task in which they attempt to 'catch' moving targets in order to determine whether stripe orientation affects capture success, as previous research has suggested that different stripe orientations may be processed differently by the visual system. We also ask whether increasing the number of targets presented in a trial can affect capture success, as previous research has suggested that motion dazzle effects may be larger in groups. RESULTS: When single targets were presented sequentially within each trial, we find that perpendicular and oblique striped targets are captured at a similar rate to uniform grey targets, but parallel striped targets are significantly easier to capture. However, when multiple targets are present simultaneously during a trial we find that striped targets are captured in fewer attempts and more quickly than grey targets. CONCLUSIONS: Our results suggest that there may be differences in capture success based on target pattern orientation, perhaps suggesting that different visual mechanisms are involved in processing of parallel stripes compared to perpendicular/oblique stripes. However, these results do not seem to generalise to trials with multiple targets, and contrary to previous predictions, striped targets appear to be easier to capture when multiple targets are present compared to being presented individually. These results suggest that the different orientations of stripes seen on animals in nature (such as in fish and snakes) may serve different purposes, and that it is unclear whether motion dazzle effects may have greater benefits for animals living in groups.We thank the subjects who volunteered to take part in these experiments.AEH was supported by a BBSRC CASE studentship and MS was supported by a Biotechnology and Biological Sciences Research Council (BBSRC) David Phillips Research Fellowship (BB/G022887/1).This is the final version of the article. It first appeared from BioMed Central via http://dx.doi.org/10.1186/s12983-015-0110-

Motion dazzle and the effects of target patterning on capture success.

BACKGROUND: Stripes and other high contrast patterns found on animals have been hypothesised to cause "motion dazzle", a type of defensive coloration that operates when in motion, causing predators to misjudge the speed and direction of object movement. Several recent studies have found some support for this idea, but little is currently understood about the mechanisms underlying this effect. Using humans as model 'predators' in a touch screen experiment we investigated further the effectiveness of striped targets in preventing capture, and considered how stripes compare to other types of patterning in order to understand what aspects of target patterning are important in making a target difficult to capture. RESULTS: We find that striped targets are among the most difficult to capture, but that other patterning types are also highly effective at preventing capture in this task. Several target types, including background sampled targets and targets with a 'spot' on were significantly easier to capture than striped targets. We also show differences in capture attempt rates between different target types, but we find no differences in learning rates between target types. CONCLUSIONS: We conclude that striped targets are effective in preventing capture, but are not uniquely difficult to catch, with luminance matched grey targets also showing a similar capture rate. We show that key factors in making capture easier are a lack of average background luminance matching and having trackable 'features' on the target body. We also find that striped patterns are attempted relatively quickly, despite being difficult to catch. We discuss these findings in relation to the motion dazzle hypothesis and how capture rates may be affected more generally by pattern type.AEH received a studentship from the BBSRC and a CASE award from Dstl, Portsdown West, UK. MS and JT were supported by a Biotechnology and Biological Sciences Research Council, David Phillips Research Fellowship (BB/G022887/1).This is the final published version. It is published by BioMed Central in BMC Evolutionary Biology here: http://www.biomedcentral.com/1471-2148/14/201

Defeating crypsis: detection and learning of camouflage strategies.

Camouflage is perhaps the most widespread defence against predators in nature and an active area of interdisciplinary research. Recent work has aimed to understand what camouflage types exist (e.g. background matching, disruptive, and distractive patterns) and their effectiveness. However, work has almost exclusively focused on the efficacy of these strategies in preventing initial detection, despite the fact that predators often encounter the same prey phenotype repeatedly, affording them opportunities to learn to find those prey more effectively. The overall value of a camouflage strategy may, therefore, reflect both its ability to prevent detection by predators and resist predator learning. We conducted four experiments with humans searching for hidden targets of different camouflage types (disruptive, distractive, and background matching of various contrast levels) over a series of touch screen trials. As with previous work, disruptive coloration was the most successful method of concealment overall, especially with relatively high contrast patterns, whereas potentially distractive markings were either neutral or costly. However, high contrast patterns incurred faster decreases in detection times over trials compared to other stimuli. In addition, potentially distractive markings were sometimes learnt more slowly than background matching markings, despite being found more readily overall. Finally, learning effects were highly dependent upon the experimental paradigm, including the number of prey types seen and whether subjects encountered targets simultaneously or sequentially. Our results show that the survival advantage of camouflage strategies reflects both their ability to avoid initial detection (sensory mechanisms) and predator learning (perceptual mechanisms)

Developing a collaborative framework for naturalistic visual search

While much research has investigated the mechanisms of visual search behaviour in laboratory-based computer tasks, there has been relatively little work on whether these results generalise to more naturalistic search tasks and thus how well existing theories explain real-world search behaviour. In addition, work relating to this question has often been carried out by researchers working in very different disciplines, including not just vision science but also fields such as consumer behaviour, sports science and medical science, making it more difficult to get an overview of the progress made and open questions remaining. We present findings from a systematic review of real-world visual search, showing that we can group the current literature into theoretical and applied approaches, and that there are certain well-studied topics (e.g., X-ray screening) but that there are relatively few links made across different search tasks and/or search contexts. We also present preliminary work detailing our development of a “naturalistic search task battery”, which aims to provide a suite of open source, reproducible and standardised real-world search tasks, thus enabling the generation of comparable data across multiple studies and aiding theory and modelling in this area

The Bulletin, School of Nursing Diploma Program Alumni Association, 1980

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Helping students see eye to eye: Diversifying teaching of sensation and perception in higher education

There is current interest in diversifying teaching curricula across many disciplines in university teaching. Sensation and perception is often considered difficult to diversify. Current challenges include diversity of the topics and teaching tools/materials, and the diversity that characterizes both the student and the teacher populations. We start by describing the diversity present in student and teacher groups, with a UK focus, and discuss how inclusive and diverse teaching materials can impact participation and engagement of broad student groups. We next consider how teaching content can be broadened by teaching on topics that consider differences between participant groups with different characteristics (including gender, ethnicity, disability and culture). Finally, we suggest resources that can be used to diversify sensation and perception teaching. We include example topics where diversity features in perception research, aimed at engaging teachers and students in the process of diversifying the teaching of sensation and perception

The evolution of patterning during movement in a large-scale citizen science game.

The motion dazzle hypothesis posits that high contrast geometric patterns can cause difficulties in tracking a moving target and has been argued to explain the patterning of animals such as zebras. Research to date has only tested a small number of patterns, offering equivocal support for the hypothesis. Here, we take a genetic programming approach to allow patterns to evolve based on their fitness (time taken to capture) and thus find the optimal strategy for providing protection when moving. Our 'Dazzle Bug' citizen science game tested over 1.5 million targets in a touch screen game at a popular visitor attraction. Surprisingly, we found that targets lost pattern elements during evolution and became closely background matching. Modelling results suggested that targets with lower motion energy were harder to catch. Our results indicate that low contrast, featureless targets offer the greatest protection against capture when in motion, challenging the motion dazzle hypothesis

Population receptive field estimates for motion-defined stimuli.

The processing of motion changes throughout the visual hierarchy, from spatially restricted 'local motion' in early visual cortex to more complex large-field 'global motion' at later stages. Here we used functional magnetic resonance imaging (fMRI) to examine spatially selective responses in these areas related to the processing of random-dot stimuli defined by differences in motion. We used population receptive field (pRF) analyses to map retinotopic cortex using bar stimuli comprising coherently moving dots. In the first experiment, we used three separate background conditions: no background dots (dot-defined bar-only), dots moving coherently in the opposite direction to the bar (kinetic boundary) and dots moving incoherently in random directions (global motion). Clear retinotopic maps were obtained for the bar-only and kinetic-boundary conditions across visual areas V1-V3 and in higher dorsal areas. For the global-motion condition, retinotopic maps were much weaker in early areas and became clear only in higher areas, consistent with the emergence of global-motion processing throughout the visual hierarchy. However, in a second experiment we demonstrate that this pattern is not specific to motion-defined stimuli, with very similar results for a transparent-motion stimulus and a bar defined by a static low-level property (dot size) that should have driven responses particularly in V1. We further exclude explanations based on stimulus visibility by demonstrating that the observed differences in pRF properties do not follow the ability of observers to localise or attend to these bar elements. Rather, our findings indicate that dorsal extrastriate retinotopic maps may primarily be determined by the visibility of the neural responses to the bar relative to the background response (i.e. neural signal-to-noise ratios) and suggests that claims about stimulus selectivity from pRF experiments must be interpreted with caution