Two-Channel Passive Detection Exploiting Cyclostationarity

This paper addresses a two-channel passive detection problem exploiting cyclostationarity. Given a reference channel (RC) and a surveillance channel (SC), the goal is to detect a target echo present at the surveillance array transmitted by an illuminator of opportunity equipped with multiple antennas. Since common transmission signals are cyclostationary, we exploit this information at the detector. Specifically, we derive an asymptotic generalized likelihood ratio test (GLRT) to detect the presence of a cyclostationary signal at the SC given observations from RC and SC. This detector tests for different covariance structures. Simulation results show good performance of the proposed detector compared to competing techniques that do not exploit cyclostationarity

Dwelling on simple stimuli in visual search

Research and theories on visual search often focus on visual guidance to explain differences in search. Guidance is the tuning of attention to target features and facilitates search because distractors that do not show target features can be more effectively ignored (skipping). As a general rule, the better the guidance is, the more efficient search is. Correspondingly, behavioral experiments often interpreted differences in efficiency as reflecting varying degrees of attentional guidance. But other factors such as the time spent on processing a distractor (dwelling) or multiple visits to the same stimulus in a search display (revisiting) are also involved in determining search efficiency. While there is some research showing that dwelling and revisiting modulate search times in addition to skipping, the corresponding studies used complex naturalistic and category-defined stimuli. The present study tests whether results from prior research can be generalized to more simple stimuli, where target-distractor similarity, a strong factor influencing search performance, can be manipulated in a detailed fashion. Thus, in the present study, simple stimuli with varying degrees of target-distractor similarity were used to deliver conclusive evidence for the contribution of dwelling and revisiting to search performance. The results have theoretical and methodological implications: They imply that visual search models should not treat dwelling and revisiting as constants across varying levels of search efficiency and that behavioral search experiments are equivocal with respect to the responsible processing mechanisms underlying more versus less efficient search. We also suggest that eye-tracking methods may be used to disentangle different search components such as skipping, dwelling, and revisiting

Parola parlata: convenzioni e tecniche di resa nella narrativa araba classica

Numero monografico: L’oralità nella scrittura. Modalità di rappresentazione della parola orale nel testo scritto”, a cura di Maria Teresa Biaso

Distractor Dwelling, Skipping, and Revisiting Determine Target Absent Performance in Difficult Visual Search

Horstmann G, Herwig A, Becker SI. Distractor Dwelling, Skipping, and Revisiting Determine Target Absent Performance in Difficult Visual Search. Frontiers in Psychology. 2016;7: 1152.Some targets in visual search are more difficult to find than others. In particular, a target that is similar to the distractors is more difficult to find than a target that is dissimilar to the distractors. Efficiency differences between easy and difficult searches are manifest not only in target-present trials but also in target-absent trials. In fact, even physically identical displays are searched through with different efficiency depending on the searched-for target. Here, we monitored eye movements in search for a target similar to the distractors (difficult search) versus a target dissimilar to the distractors (easy search). We aimed to examine three hypotheses concerning the causes of differential search efficiencies in target-absent trials: (a) distractor dwelling (b) distractor skipping, and (c) distractor revisiting. Reaction times increased with target similarity which is consistent with existing theories and replicates earlier results. Eye movement data indicated guidance in target trials, even though search was very slow. Dwelling, skipping, and revisiting contributed to low search efficiency in difficult search, with dwelling being the strongest factor. It is argued that differences in dwell time account for a large amount of total search time differences

Threat captures attention, but not automatically: Top-down goals modulate attentional orienting to threat distractors

The rapid orienting of attention to potential threats has been proposed to proceed outside of top-down control. However, paradigms that have been used to investigate this have struggled to separate the rapid orienting of attention (i.e. capture) from the later disengagement of focal attention that may be subject to top-down control. Consequently, it remains unclear whether and to what extent orienting to threat is contingent on top-down goals. The current study manipulated the goal-relevance of threat distractors (spiders), whilst a strict top-down attentional set was encouraged by presenting the saliently colored target and the threat distracter simultaneously for a limited time. The goal-relevance of threatening distractors was manipulated by including a spider amongst the possible target stimuli (Experiment 1: spider/cat targets) or excluding it (Experiment 2: bird/fish targets). Orienting and disengagement were disentangled by cueing attention away from or towards the threat prior to its onset. The results indicated that the threatening spider distractors elicited rapid orienting of attention when spiders were potentially goal-relevant (Experiment 1) but did so much less when they were irrelevant to the task goal (Experiment 2). Delayed disengagement from the threat distractors was even more strongly contingent on the task goal and occurred only when a spider was a possible target. These results highlight the role of top-down goals in attentional orienting to and disengagement from threat. © 2016 The Psychonomic Society, Inc

Joint Detection of Almost-Cyclostationary Signals and Estimation of Their Cycle Period

We propose a technique that jointly detects the presence of almost-cyclostationary (ACS ) signals in wide-sense stationary noise and provides an estimate of their cycle period. Since the cycle period of an ACS process is not an integer, the approach is based on a combination of a resampling stage and a multiple hypothesis test, which deal separately with the fractional part and the integer part of the cycle period. The approach requires resampling the signal at many different rates, which is computationally expensive. For this reason, we propose a filter hank structure that allows us to efficiently resample a signal at many different rates by identifying common interpolation stages among the set of resampling rates.The work of D. Ram ́ırez was supported in part by the Ministerio de Econom ́ıaof Spain under projects: OTOSIS (TEC2013-41718-R) and the COMONSENSNetwork (TEC2015-69648-REDC), in part by the Ministerio de Econom ́ıa ofSpain jointly with the European Commission (ERDF) under projects ADVEN-TURE (TEC2015-69868-C2-1-R) and CAIMAN (TEC2017-86921-C2-2-R), inpart by the Comunidad de Madrid under project CASI-CAM-CM (S2013/ICE-2845), and in part by the German Research Foundation (DFG) under projectRA 2662/2-1. The work of S. Horstmann and P. J. Schreier were supported bythe German Research Foundation (DFG) under Grant SCHR 1384/6-

More Efficient Visual Search for Happy Faces May Not Indicate Guidance, but Rather Faster Distractor Rejection: Evidence From Eye Movements and Fixations

Horstmann G, Becker SI. More Efficient Visual Search for Happy Faces May Not Indicate Guidance, but Rather Faster Distractor Rejection: Evidence From Eye Movements and Fixations. EMOTION. 2020;20(2):206-216.The visual search paradigm has been used in emotion research to examine the relation between facial expressions of emotion and attention. Here, the better performance in a search for one facial expression category (e.g., a happy face) compared to a second category (e.g., an angry face) has been often interpreted as indicating better guidance of attention. Better guidance of attention in turn indicates that some aspect of the facial expression can be used preattentively, that is, while focused attention is directed elsewhere in the visual field. This view has been criticized because better performance may also mean better distractor rejection independently of guidance. The present study uses eye tracking to disentangle the two variables. The results show better search performance with a happy than angry face as the target. Facial emotion also influenced the time the eyes fixated a stimulus (dwelling), but not guidance related variables of search performance. A linear regression moreover showed that dwelling accounted for large amounts of variance in the overall search times. Overall, the results present clear-cut evidence that differential search performance does not need to indicate differential guidance, but may also be explained by postselective factors that influence the dwelling on stimuli. The broader implication of this demonstration is that results from the visual search paradigm have to be interpreted with caution, and that better search performance cannot be directly interpreted as an indicator of preattentive guidance of attention

Attentional effects of negative faces: Top-down contingent or involuntary?

Horstmann G, Becker SI. Attentional effects of negative faces: Top-down contingent or involuntary? PERCEPTION & PSYCHOPHYSICS. 2008;70(8):1416-1434.Recent research has substantiated that schematic negative faces are found more efficiently than positive faces among crowds of distractor faces of varying set sizes. The present study asks whether this relative search asymmetry (RSA) is intention driven or due to involuntary attentional capture. To that aim, participants were fist tested in a condition in which negative and positive faces were searched for, and then in a condition in which negative or positive schematic faces appeared at chance level at the position of the target (valid trials) or of a distractor (invalid trials), the faces thus being task irrelevant (the 1/n paradigm). The expected search benefit for valid negative-face target trials most clearly occurred when participants searched for a target defined by a conjunction of color and position; when the target was defined either by an orientation or color singleton, we found rather weak or no evidence for involuntary attention capture by negative faces. We see the results as being (1) evidence that the RSA is partly based on stimulus-driven factors that occur independently of the intention to search for a positive or negative face, and (2) consistent with the assumption that the effects are mainly due to a more efficient rejection of positive-face than of negative-face distractors, rather than being due to attentional capture by the target