Items that stand out from their surroundings, that is, those that attract attention, are considered to be salient. Salience is generated by input features in many stimulus dimensions, like motion (M), color (C), orientation (O), and others. We focus on bottom-up salience generated by contrast between the feature properties of an item and its surroundings. We compare the singleton search reaction times (RTs) of items that differ from their surroundings in more than one feature (e.g., C + O, denoted as CO) against the RTs of items that differ from their surroundings in only a single feature (e.g., O or C). The measured RTs for the double-feature singletons are compared against "race model" predictions to evaluate whether salience in the double-feature conditions is greater than the salience of either of its feature components. Affirmative answers were found in MO and CO but not in CM. These results are consistent with some V1 neurons being conjunctively selective to MO, others to CO, but almost none to CM. They provide support for the V1 hypothesis of bottom-up salience (Z. Li, 2002) but are contrary to expectation from the "feature summation" hypothesis, in which different stimulus features are initially analyzed independently and subsequently summed to form a single salience map (L. Itti & C. Koch, 2001; C. Koch & S. Ullman, 1985; J. M. Wolfe, K. R. Cave, & S. L. Franzel, 1989).

We examined whether the detection of audio-visual temporal synchrony is determined by a pre-attentive parallel process, or by an attentive serial process using a visual search paradigm. We found that detection of a visual target that changed in synchrony with an auditory stimulus was gradually impaired as the number of unsynchronized visual distractors increased (experiment 1), whereas synchrony discrimination of an attended target in a pre-cued location was unaffected by the presence of distractors (experiment 2). The effect of distractors cannot be ascribed to reduced target visibility nor can the increase in false alarm rates be predicted by a noisy parallel processing model. Reaction times for target detection increased linearly with number of distractors, with the slope being about twice as steep for target-absent trials as for targetpresent trials (experiment 3). Similar results were obtained regardless of whether the audio-visual stimulus consisted of visual flashes synchronized with amplitude-modulated pips, or of visual rotations synchronized with frequency-modulated up-down sweeps. All of the results indicate that audio-visual perceptual synchrony is judged by a serial process and are consistent with the suggestion that audio-visual temporal synchrony is detected by a 'mid-level' feature matching process.

Retinal velocity distributions can lead to a percept of three-dimensional (3D) structure (structure-from-motion [SFM]). SFM stimuli are intrinsically ambiguous with regard to depth ordering. A classic example is the orthographic projection of a revolving transparent cylinder, which can be perceived as a 3D cylinder that rotates clockwise and counterclockwise alternately. Prevailing models attribute such bistable percepts to inhibitory connections between neurons that are tuned to opposite motion directions at equal binocular disparities. Cylinder stimuli can yield not only two but as many as four different percepts. Besides the well-documented clockwise and counterclockwise spinning transparent cylinders, observers can also perceive two transparent half-cylinders, either convex or concave, one in front of the other. Observers are able to bias the time during which a percept is present by attending to one or the other percept. We examined this phenomenon quantitatively and found that in standard SFM stimuli, the percept of two convex transparent half-cylinders can occur just as often as the percept of (counter-) clockwise spinning cylinders. So far, however, all interpretations of experimental (neurophysiological) data and all proposed mechanisms for SFM perception have focused solely on the two classical cylinder percepts. Prevailing models cannot explain the existence of the other two percepts. We suggest an alternative model to explain attention-biased multi-stable perception.

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Abstract-This article presents the implementation and experimental validation of a control system dedicated to human robot physical interaction during object handovers. Our control law defines the trajectory of the robotic arm towards a previously unknown handover location based on the Dynamic Movement Primitives formalism adapted for human robot object handover. The control law was deployed on a Kuka Light-Weight Arm equipped with the Azzurra anthropomorphic hand. We employed an industrial-like setting involving three different human postures for object handover in order to evaluate the performance and user experience of our control law and its generalizability. The evaluation was conducted over 1000 object handover trials between the human and robot partners, and the kinematic data and subjective experience were gathered for each trial. The outcomes of this evaluation validate the current implementation and guide the next steps towards more efficient and fluid human robot interaction.