Assessing the time course and magnitude of different forms of attentional priming.

Priming of attentional selection involves speeded selection of task-relevant visual search items when search stimuli remain constant between trials. Various paradigms involving different features have been used to study the nature of this priming. The tasks differ greatly in difficulty and the neural mechanisms involved, raising the question of how easily priming on one feature dimension can be used to draw conclusions about priming on another. Here, this was addressed by contrasting time courses and relative sizes of priming effects for the repetition of a lower-level and higher-level feature (color vs. facial expression). Priming was tested in two odd-one-out search tasks, one involving discrimination (experiments 1A and 1B), the other a present/absent judgment (experiments 2A and 2B). The main question was how similar the size and temporal profiles of priming are for the two features. The sizes of the priming effects were very different for color and expression and color priming effects lasted for much longer than expression priming (measured with memory kernel analyses), suggesting that the mechanisms behind the effects differ in their operational principles. Different forms of priming should only be compared with great caution and priming seems to occur at many levels of processing. Priming should be thought of as a general principle of perceptual processing.

Contrasting attentional biases in a saccadic choice task.

To gain insight into how human observers select items in the visual field we pitted two attentional biases against one another in a single free choice design. The first bias is the nasal-temporal asymmetry during free choice tasks, where observers tend to choose targets that appear in their temporal hemifield over targets appearing in their nasal hemifield. The second is the choice bias found in studies of attentional priming. When observers have to select between a stimulus that shares features with a preceding target and a stimulus sharing features with previous distractors, they have a strong tendency to choose the preceding search target and this bias increases the more often the same search is repeated. Our results show that both biases affect saccadic choice, but they also show that the nasal-temporal bias can modulate the strength of the priming effects, but not vice versa. The priming effect was stronger for stimuli appearing in the temporal than in the nasal hemifield, but the nasal-temporal bias was similar for primed and unprimed targets. Additionally, our findings are the first to show how search repetition leads to faster saccades. The observed difference between the effects of the NTA and priming biases may reflect the difference in neural mechanisms thought to be behind these biases and that biases at lower levels may outrank higher-level biases, at least in their effect on visual attention.

No Advantage for Separating Overt and Covert Attention in Visual Search.

We move our eyes roughly three times every second while searching complex scenes, but covert attention helps to guide where we allocate those overt fixations. Covert attention may be allocated reflexively or voluntarily, and speeds the rate of information processing at the attended location. Reducing access to covert attention hinders performance, but it is not known to what degree the locus of covert attention is tied to the current gaze position. We compared visual search performance in a traditional gaze-contingent display, with a second task where a similarly sized contingent window is controlled with a mouse, allowing a covert aperture to be controlled independently by overt gaze. Larger apertures improved performance for both the mouse- and gaze-contingent trials, suggesting that covert attention was beneficial regardless of control type. We also found evidence that participants used the mouse-controlled aperture somewhat independently of gaze position, suggesting that participants attempted to untether their covert and overt attention when possible. This untethering manipulation, however, resulted in an overall cost to search performance, a result at odds with previous results in a change blindness paradigm. Untethering covert and overt attention may therefore have costs or benefits depending on the task demands in each case.

Asymmetries of the visual system and their influence on visual performance and oculomotor dynamics.

Our representation of the visual field is not homogenous. There are differences in resolution not only between the fovea and regions eccentric to it, but also between the nasal and temporal hemiretinae, that can be traced to asymmetric distributions of photoreceptors and ganglion cells. We review evidence for differences in visual and attentional processing and oculomotor behaviour that can be traced to asymmetries of the visual system, mainly emphasising nasal-temporal asymmetries. Asymmetries in the visual system manifest in various measures, in basic psychophysical tests of visual performance, attentional processing, choice behaviour, saccadic peak velocity, and latencies. Nasal-temporal asymmetries on saccadic latency seem primarily to occur for express saccades. Neural asymmetries between the upper and lower hemifields are strong and cause corresponding differences in performance between the hemifields. There are interesting individual differences in asymmetric processing which seem to be related to the strength of eye dominance. These neurophysiological asymmetries and the corresponding asymmetries in visual performance and oculomotor behaviour can strongly influence experimental results in vision and must be considered during experimental design and the interpretation of results.

Measuring relative vibrotactile spatial acuity: effects of tactor type, anchor points and tactile anisotropy.

Vibrotactile displays can compensate for the loss of sensory function of people with permanent or temporary deficiencies in vision, hearing, or balance, and can augment the immersive experience in virtual environments for entertainment, or professional training. This wide range of potential applications highlights the need for research on the basic psychophysics of mechanisms underlying human vibrotactile perception. One key consideration when designing tactile displays is determining the minimal possible spacing between tactile motors (tactors), by empirically assessing the maximal throughput of the skin, or, in other words, vibrotactile spatial acuity. Notably, such estimates may vary by tactor type. We assessed vibrotactile spatial acuity in the lower thoracic region for three different tactor types, each mounted in a 4 × 4 array with center-to-center inter-tactor distances of 25 mm, 20 mm, and 10 mm. Seventeen participants performed a relative three-alternative forced-choice point localization task with successive tactor activation for both vertical and horizontal stimulus presentation. The results demonstrate that specific tactor characteristics (frequency, acceleration, contact area) significantly affect spatial acuity measurements, highlighting that the results of spatial acuity measurements may only apply to the specific tactors tested. Furthermore, our results reveal an anisotropy in vibrotactile perception, with higher spatial acuity for horizontal than for vertical stimulus presentation. The findings allow better understanding of vibrotactile spatial acuity and can be used for formulating guidelines for the design of tactile displays, such as regarding inter-tactor spacing, choice of tactor type, and direction of stimulus presentation.

Effects of saccade training on express saccade proportions, saccade latencies, and peak velocities: an investigation of nasal/temporal differences.

Express saccades have very short latencies and are often considered a special population of saccadic eye movements. Recent evidence suggests that express saccade generation in humans increases with training, and that this training is independent of the actual saccade vector being trained. We assessed the time course of these training-induced increases in express saccade generation and how they differ between the nasal and temporal hemifields, and second whether they transfer from the trained to the untrained eye. We also measured the effects of training on saccade latencies more generally, and upon peak velocities. The training effect transferred between the nasal and temporal hemifields and between the trained and untrained eyes. More surprisingly, we found an asymmetric effect of training on express saccade proportions: Before training, express saccade proportions were higher for saccades made into the nasal hemifield but with training this reversed. This training-induced asymmetry was also observed in overall saccade latencies, showing how training can unmask nasal/temporal asymmetries in saccade latencies. Finally, we report for the first time that saccadic peak velocities increased with training, independently of changes in amplitude.

Implicit processing during change blindness revealed with mouse-contingent and gaze-contingent displays.

People often miss salient events that occur right in front of them. This phenomenon, known as change blindness, reveals the limits of visual awareness. Here, we investigate the role of implicit processing in change blindness using an approach that allows partial dissociation of covert and overt attention. Traditional gaze-contingent paradigms adapt the display in real time according to current gaze position. We compare such a paradigm with a newly designed mouse-contingent paradigm where the visual display changes according to the real-time location of a user-controlled mouse cursor, effectively allowing comparison of change detection with mainly overt attention (gaze-contingent display; Experiment 2) and untethered overt and covert attention (mouse-contingent display; Experiment 1). We investigate implicit indices of target detection during change blindness in eye movement and behavioral data, and test whether affective devaluation of unnoticed targets may contribute to change blindness. The results show that unnoticed targets are processed implicitly, but that the processing is shallower than if the target is consciously detected. Additionally, the partial untethering of covert attention with the mouse-contingent display changes the pattern of search and leads to faster detection of the changing target. Finally, although it remains possible that the deployment of covert attention is linked to implicit processing, the results fall short of establishing a direct connection.

Timed written picture naming in 14 European languages.

We describe the Multilanguage Written Picture Naming Dataset. This gives trial-level data and time and agreement norms for written naming of the 260 pictures of everyday objects that compose the colorized Snodgrass and Vanderwart picture set (Rossion & Pourtois in Perception, 33, 217-236, 2004). Adult participants gave keyboarded responses in their first language under controlled experimental conditions (N = 1,274, with subsamples responding in Bulgarian, Dutch, English, Finnish, French, German, Greek, Icelandic, Italian, Norwegian, Portuguese, Russian, Spanish, and Swedish). We measured the time to initiate a response (RT) and interkeypress intervals, and calculated measures of name and spelling agreement. There was a tendency across all languages for quicker RTs to pictures with higher familiarity, image agreement, and name frequency, and with higher name agreement. Effects of spelling agreement and effects on output rates after writing onset were present in some, but not all, languages. Written naming therefore shows name retrieval effects that are similar to those found in speech, but our findings suggest the need for cross-language comparisons as we seek to understand the orthographic retrieval and/or assembly processes that are specific to written output.

Relative vibrotactile spatial acuity of the torso.

While tactile acuity for pressure has been extensively investigated, far less is known about acuity for vibrotactile stimulation. Vibrotactile acuity is important however, as such stimulation is used in many applications, including sensory substitution devices. We tested discrimination of vibrotactile stimulation from eccentric rotating mass motors with in-plane vibration. In 3 experiments, we tested gradually decreasing center-to-center (c/c) distances from 30 mm (experiment 1) to 13 mm (experiment 3). Observers judged whether a second vibrating stimulator ('tactor') was to the left or right or in the same place as a first one that came on 250 ms before the onset of the second (with a 50-ms inter-stimulus interval). The results show that while accuracy tends to decrease the closer the tactors are, discrimination accuracy is still well above chance for the smallest distance, which places the threshold for vibrotactile stimulation well below 13 mm, which is lower than recent estimates. The results cast new light on vibrotactile sensitivity and can furthermore be of use in the design of devices that convey information through vibrotactile stimulation.

Designing sensory-substitution devices: Principles, pitfalls and potential1.

An exciting possibility for compensating for loss of sensory function is to augment deficient senses by conveying missing information through an intact sense. Here we present an overview of techniques that have been developed for sensory substitution (SS) for the blind, through both touch and audition, with special emphasis on the importance of training for the use of such devices, while highlighting potential pitfalls in their design. One example of a pitfall is how conveying extra information about the environment risks sensory overload. Related to this, the limits of attentional capacity make it important to focus on key information and avoid redundancies. Also, differences in processing characteristics and bandwidth between sensory systems severely constrain the information that can be conveyed. Furthermore, perception is a continuous process and does not involve a snapshot of the environment. Design of sensory substitution devices therefore requires assessment of the nature of spatiotemporal continuity for the different senses. Basic psychophysical and neuroscientific research into representations of the environment and the most effective ways of conveying information should lead to better design of sensory substitution systems. Sensory substitution devices should emphasize usability, and should not interfere with other inter- or intramodal perceptual function. Devices should be task-focused since in many cases it may be impractical to convey too many aspects of the environment. Evidence for multisensory integration in the representation of the environment suggests that researchers should not limit themselves to a single modality in their design. Finally, we recommend active training on devices, especially since it allows for externalization, where proximal sensory stimulation is attributed to a distinct exterior object.

Visual Foraging With Fingers and Eye Gaze.

A popular model of the function of selective visual attention involves search where a single target is to be found among distractors. For many scenarios, a more realistic model involves search for multiple targets of various types, since natural tasks typically do not involve a single target. Here we present results from a novel multiple-target foraging paradigm. We compare finger foraging where observers cancel a set of predesignated targets by tapping them, to gaze foraging where observers cancel items by fixating them for 100 ms. During finger foraging, for most observers, there was a large difference between foraging based on a single feature, where observers switch easily between target types, and foraging based on a conjunction of features where observers tended to stick to one target type. The pattern was notably different during gaze foraging where these condition differences were smaller. Two conclusions follow: (a) The fact that a sizeable number of observers (in particular during gaze foraging) had little trouble switching between different target types raises challenges for many prominent theoretical accounts of visual attention and working memory. (b) While caveats must be noted for the comparison of gaze and finger foraging, the results suggest that selection mechanisms for gaze and pointing have different operational constraints.

The Sound of Vision Project: On the Feasibility of an Audio-Haptic Representation of the Environment, for the Visually Impaired.

The Sound of Vision project involves developing a sensory substitution device that is aimed at creating and conveying a rich auditory representation of the surrounding environment to the visually impaired. However, the feasibility of such an approach is strongly constrained by neural flexibility, possibilities of sensory substitution and adaptation to changed sensory input. We review evidence for such flexibility from various perspectives. We discuss neuroplasticity of the adult brain with an emphasis on functional changes in the visually impaired compared to sighted people. We discuss effects of adaptation on brain activity, in particular short-term and long-term effects of repeated exposure to particular stimuli. We then discuss evidence for sensory substitution such as Sound of Vision involves, while finally discussing evidence for adaptation to changes in the auditory environment. We conclude that sensory substitution enterprises such as Sound of Vision are quite feasible in light of the available evidence, which is encouraging regarding such projects.

Translational research-the need of a new bioethics approach.

Translational research tries to apply findings from basic science to enhance human health and well-being. Many phases of the translational research may include non-medical tasks (information technology, engineering, nanotechnology, biochemistry, animal research, economy, sociology, psychology, politics, and so on). Using common bioethics principles to these areas might sometimes be not feasible, or even impossible. However, the whole process must respect some fundamental, moral principles. The purpose of this paper is to argument the need for a different approach to the morality in translational bioethics, and to suggest some directions that might be followed when constructing such a bioethics. We will show that a new approach is needed and present a few ethical issues that are specific to the translational research.

Understanding visual attention in childhood: Insights from a new visual foraging task.

A recently developed visual foraging task, involving multiple targets of different types, can provide a rich and dynamic picture of visual attention performance. We measured the foraging performance of 66 children aged 4-7 years, along with measures of two conceptually related constructs, self-regulation and verbal working memory. Our results show that foraging patterns of young children differ from adult patterns. Children have difficulty with foraging for two target types, not only when they are defined by a conjunction of features but, unlike adults, also when they forage simultaneously for two target types that are distinguished from distractors by a single feature. Importantly, such feature/conjunction differences between adults and children are not seen in more traditional single-target visual search tasks. Interestingly, the foraging patterns of the youngest children were slightly more adult-like than of the oldest ones, which may suggest that older children attempt to use strategies that they have not yet fully mastered. The older children were, however, able to complete more trials, during both feature and conjunction foraging. Self-regulation and verbal working memory did not seem to affect foraging strategies, but both were connected with faster and more efficient foraging. We propose that our visual foraging paradigm is a promising avenue for studying the development of visual cognitive abilities.

Blaming the victims of your own mistakes: How visual search accuracy influences evaluation of stimuli.

Even without explicit positive or negative reinforcement, experiences may influence preferences. According to the affective feedback in hypotheses testing account preferences are determined by the accuracy of hypotheses: correct hypotheses evoke positive affect, while incorrect ones evoke negative affect facilitating changes of hypotheses. Applying this to visual search, we suggest that accurate search should lead to more positive ratings of targets than distractors, while for errors targets should be rated more negatively. We test this in two experiments using time-limited search for a conjunction of gender and tint of faces. Accurate search led to more positive ratings for targets as compared to distractors or targets following errors. Errors led to more negative ratings for targets than for distractors. Critically, eye tracking revealed that the longer the fixation dwell times in target regions, the higher the target ratings for correct responses, and the lower the ratings for errors. The longer observers look at targets, the more positive their ratings if they answer correctly, and less positive, following errors. The findings support the affective feedback account and provide the first demonstration of negative effects on liking ratings following errors in visual search.

How priming in visual search affects response time distributions: analyses with ex-Gaussian fits.

Although response times (RTs) are the dependent measure of choice in the majority of studies of visual attention, changes in RTs can be hard to interpret. First, they are inherently ambiguous, since they may reflect a change in the central tendency or skew (or both) of a distribution. Second, RT measures may lack sensitivity, since meaningful changes in RT patterns may not be picked up if they reflect two or more processes having opposing influences on mean RTs. Here we describe RT distributions for repetition priming in visual search, fitting ex-Gaussian functions to RT distributions. We focus here on feature and conjunction search tasks, since priming effects in these tasks are often thought to reflect similar mechanisms. As expected, both tasks resulted in strong priming effects when target and distractor identities repeated, but a large difference between feature and conjunction search was also seen, in that the σ parameter (reflecting the standard deviation of the Gaussian component) was far more affected by search repetition in conjunction than in feature search. Although caution should clearly be used when particular parameter estimates are matched to specific functions or processes, our results suggest that analyses of RT distributions can inform theoretical accounts of priming in visual search tasks, in this case showing quite different repetition effects for the two differing search types, suggesting that priming in the two paradigms partly reflects different mechanisms.

Common attentional constraints in visual foraging.

Predators are known to select food of the same type in non-random sequences or "runs" that are longer than would be expected by chance. If prey are conspicuous, predators will switch between available sources, interleaving runs of different prey types. However, when prey are cryptic, predators tend to focus on one food type at a time, effectively ignoring equally available sources. This latter finding is regarded as a key indicator that animal foraging is strongly constrained by attention. It is unknown whether human foraging is equally constrained. Here, using a novel iPad task, we demonstrate for the first time that it is. Participants were required to locate and touch 40 targets from 2 different categories embedded within a dense field of distractors. When individual target items "popped-out" search was organized into multiple runs, with frequent switching between target categories. In contrast, as soon as focused attention was required to identify individual targets, participants typically exhausted one entire category before beginning to search for the other. This commonality in animal and human foraging is compelling given the additional cognitive tools available to humans, and suggests that attention constrains search behavior in a similar way across a broad range of species.

Modulation of antisaccade costs through manipulation of target-location probability: only under decisional uncertainty.

Latencies of antisaccades made in the direction opposite to a peripheral target are typically slower longer than of prosaccades towards such a target by 50-100 ms. Antisaccades have proved to be an important tool for diagnostic purposes in neurology, psychology and psychiatry, providing invaluable insights into attentional function, decision making and the functionality of eye movement control. Recent findings have suggested, however, that latency differences between pro- and antisaccades can be eliminated by manipulating target-location probabilities. Pro- and antisaccades were equally fast to locations where a target rarely appeared, a finding that may be of promise for more elaborate diagnoses of neurological and psychiatric illness and further understanding of the eye movement system. Here, we tested probability manipulations for a number of different pro- and antisaccade tasks of varied difficulty. Probability only modulated antisaccade costs in a difficult antisaccade task involving decisional uncertainty with low target saliency. For other tasks including standard ones from the literature, target-location probability asymmetries had minimal effects. Probability modulation of antisaccade costs may therefore reflect effects upon decision making rather than saccade generation. This may limit the usefulness of probability manipulations of antisaccades for diagnostic purposes in neurology, psychology and related disciplines.

Searching for bumps and ellipses on the ground and in the sky: no advantage for the ground plane.

A staple of modern theories of vision is that the visual system has evolved to perceive cues containing the most predictive information about the layout of the environment. This entails the prediction that - other things being equal - visual performance in a familiar setting should be superior to performance in an unfamiliar one. Visual performance should therefore be better on the familiar ground plane compared to an implied sky or wall plane. We tested this comparing visual search for stimuli presented in an implied ground plane with search on a 180° rotated search display so that the stimuli appeared in an implied "sky" plane, and with search in a random layout implying no depth. This was tested for stimuli with, or without, curvature discontinuities, that have previously been shown to be strong cues for shape analysis. Surprisingly, no advantage of the ground plane over the sky plane was observed, while a strong effect of layout regularity was seen. Similarly, in experiment 2 there was little effect of placing the stimuli on an implied wall plane compared to the ground or the sky. The results are not explained by assuming that curvature discontinuities are such strong cues that they overshadow any effect of depth-plane, since there was a strong effect of regular versus random layout, which should also have disappeared under this account. The results argue instead for a very strong effect of layout regularity, unrelated to environmental regularities in evolutionary history, since there was no ground-plane benefit.

Violating the main sequence: asymmetries in saccadic peak velocities for saccades into the temporal versus nasal hemifields.

Saccadic peak velocities during monocular and binocular presentation were tested. While the main sequence linear increase in peak velocities as a function of saccade amplitude is well documented, our results provide demonstrations of violations of the main sequence. Peak velocities during monocular presentation were considerably higher toward temporal than nasal stimuli. This nasal-temporal asymmetry (NTA) was not explained by amplitude differences and was most pronounced for the lowest amplitudes tested, decreasing with increased amplitude. Under binocular presentation, this NTA was much smaller. While the exact reasons for this difference in peak velocities between hemifields are unclear at present, we propose that anatomical NTAs result in stronger signals from the nasal, than temporal retina leading to higher peak velocities into the temporal visual hemifield. NTAs in peak velocity are consistent with NTAs in attentional choice and in attentional function, which might also be explained by anatomical NTA.