Visual search for apparent-length targets is modulated by the Müller-Lyer illusion

Is apparent object size represented in pre-attentive vision and can it influence visual search for size-defined targets in a spatially parallel manner? This question was investigated, using the Müller-Lyer illusion. Observers searched for a target line that was longer than the distractor lines. Test lines could be presented without context arrows (control); be adjoined by obtuse-angle context arrows (arrow heads pointing inward), making the lines appear longer; or by acute-angle arrows (heads pointing outward), making the lines appear shorter. These apparent-length modulations were larger for the target than for the distractor lines, thereby increasing and, respectively, decreasing the target-distractor length contrast. In line with these changes in contrast, target detection was found to be expedited by obtuse-angle arrows and impeded by acute-angle arrows, independently of the number of elements in the display. This finding provides further evidence for the pre-attentive processing of apparent object size.     

‘Steady/equilibrium approximation’ in relaxation and fluctuation: I. Procedure to simplify first-order reaction

A general procedure to simplify a complex first-order reaction by two approximations, the principle of fast equilibration and the steady-state approximation, is presented. Rate constants are classified into two groups: those of the order of unity and those of the order of ?(? 1) or less, and are represented in the schemes by thick and thin arrows, respectively. The fast and the slow components are defined: from the fast component at least one thick arrow originates and from the slow component no thick arrow originates. Fast components are divided into several groups. In a group, the fast components are connected by thick arrows in both directions in each reaction step. When at least one thick arrow originates from the components in a group G and terminates on a component not belonging to group G (group G is open), then the steady-state approximation or principle of fast equilibration holds on each component in group G after an induction period T°. When no thick arrow originating from group G is directed to components not belonging to group G (group G is closed), the principle of fast equilibration holds on the fast components in group G after T°. The induction period T° is less than the order of I/?.     

Dynamics of temporal parameters of sensorimotor reactions in relation to the type of human movement

The study was conducted on nine right-handed male subjects 20-24 year old and consisted of two series. In the first series one warning signal in the form of one of the digits (from 1 to 8) was successively presented to the subjects on the display and then four trigger signals which required either simple pressing of the push button (an arrow with a dot) or its holding during 0.5 s (two arrows) by the right or left hand depending on the arrow direction. The digit corresponded to one variant of signals succession. Each variant was repeated randomly among other variants 15 times. In the second series instead of arrows asterisks were presented. Reaction time and duration of push button holding were recorded. Two regularities were observed: significant decrease of RT in the series of reacting by memory and successive decrease of RT in accordance with the decrease of the number of the remaining signals observed in both series. In the first series RT successively decreased by 35-40 ms, in the second one-by 16-20 ms. It is supposed that the difference in RTs between series characterizes the time of signal structure analysis, while the difference in RTs within one block of signals in the second series-the time of extraction of selected motor program from memory.     

Measurement of eye-gaze in chimpanzees (Pan troglodytes)

Gaze cues are used as an index of social cognition in primates, yet the sensitivity to different forms of gaze, and consequently the cues required to test gaze-following abilities remain understudied. Whereas the eye is attributed special signal value in humans, the camouflaged ocular morphology of non-human primates has led to the consensus that head orientation may be a more salient cue. This study presents the first documentation of the surface eye movements of the chimpanzee, Pan troglodytes, in order to determine the behavioral forms of eye-gaze and their saliency as signals, document their functional variation, and address the signal value of the eyes distinct from head orientation. Movements of the eye were identified as Scan (continuous movement), Glance (a single movement <1 sec), or Fixate (no movement). Scans, glances, and fixations were reliably detected by humans during live observation and from video (Cohen's kappa over 0.70) and, therefore, are likely also to be detected by conspecifics. Eye-gaze comprised a nonunitary measure of visual attention, reflecting the attentional task demands of different activities. Specifically, chimpanzees spent significantly more time scanning while feeding and resting, than grooming, F(2,28) = 10.23, P<0.001, and spent significantly more time fixating while grooming, than feeding or resting, F(2,28) = 7.52, P<0.01. Further, eye-gaze was often incongruent with head movement, varying significantly with the form of eye-gaze: incongruence was found during 12-21% of fixations, during 42-49% of scans, and during 70-100% of glances, F(2,16) = 30.17, P<0.001. These findings provide the basis for discrimination of the adaptive significance of gaze-processing abilities with emphasis on sensitivity to eye-gaze distinct from head orientation. If we are to continue exploring gaze-processing abilities in primates, then we need greater consideration of the precise nature of the signals themselves. Here we present evidence for special consideration of the eyes as a salient signal in P. troglodytes.     

Illustrating cerebral function: the iconography of arrows

For over a century the arrow has appeared in illustrations of cerebral function, yet the implications of using such symbols have not been previously considered. This review seeks to outline the nature, evolution, applications and limitations of this deceptively simple graphic device when it is used to picture functions of the brain. The arrow is found to have been used in several different ways: as a means of endowing anatomical structures with functional properties; as a method of displaying neural function either in free-standing form or in a structural or spatial framework; as a device for correlating functional data with underlying brain topography; and as a technique for linking functions of the brain with the world outside and with various philosophical concepts. For many of these uses the essential feature of the arrow is its directional characteristic. In contrast to the line, it is direction that enables the arrow to display information about time, which in turn can be exploited to depict functional rather than structural data. However, the use of the arrow is fraught with difficulties. It is often unclear whether an arrow has been used to illustrate fact, hypothesis, impression or possibility, or merely to provide a decorative flourish. Furthermore, the powerful symbolic nature of the arrow can so easily confer a spurious validity on the conjectural. Increasingly now there are insuperable difficulties when attempting to illustrate complex mechanisms of brain function. In the iconography of cerebral function, therefore, arrows with all their ambiguities may in certain circumstances become superseded by more non-representational symbols such as the abstract devices of the computational neuroscientist.     

Grooved Stones from Zawi Chemi Shanidar, a Protoneolithic Site in Northern Iraq

Grooved stones appear as a new cultural element in Epipaleolithic-Protoneolithic sites (dating from ca. 9000–6000 B.C.) in a broad geographic zone from Southwest Asia to North Africa. Similar objects have been recorded from archeological and ethnographic contexts in both the Old World and the New World. Ethnographic and other evidence has shown that the several types of grooved stones are associated with a variety of functions, mainly related to the manufacture and use of arrows and arrow shafts. It is suggested that these tools may be associated with the discovery and diffusion of the bow and arrow .     

Subtle cues of predation risk: starlings respond to a predator's direction of eye-gaze

For prey animals to negotiate successfully the fundamental trade-off between predation and starvation, a realistic assessment of predation risk is vital. Prey responses to conspicuous indicators of risk (such as looming predators or fleeing conspecifics) are well documented, but there should also be strong selection for the detection of more subtle cues. A predator's head orientation and eye-gaze direction are good candidates for subtle but useful indicators of risk, since many predators orient their head and eyes towards their prey as they attack. We describe the first explicit demonstration of a bird responding to a live predator's eye-gaze direction. We present wild-caught European starlings (Sturnus vulgaris) with human 'predators' whose frontal appearance and gaze direction are manipulated independently, and show that starlings are sensitive to the predator's orientation, the presence of eyes and the direction of eye-gaze. Starlings respond in a functionally significant manner: when the predator's gaze was averted, starlings resumed feeding earlier, at a higher rate and consumed more food overall. By correctly assessing lower risk and returning to feeding activity earlier (as in this study), the animal gains a competitive advantage over conspecifics that do not respond to the subtle predator cue in this way.     

Loneliness and Hypervigilance to Social Cues in Females: An Eye-Tracking Study

The goal of the present study was to examine whether lonely individuals differ from nonlonely individuals in their overt visual attention to social cues. Previous studies showed that loneliness was related to biased post-attentive processing of social cues (e.g., negative interpretation bias), but research on whether lonely and nonlonely individuals also show differences in an earlier information processing stage (gazing behavior) is very limited. A sample of 25 lonely and 25 nonlonely students took part in an eye-tracking study consisting of four tasks. We measured gazing (duration, number of fixations and first fixation) at the eyes, nose and mouth region of faces expressing emotions (Task 1), at emotion quadrants (anger, fear, happiness and neutral expression) (Task 2), at quadrants with positive and negative social and nonsocial images (Task 3), and at the facial area of actors in video clips with positive and negative content (Task 4). In general, participants tended to gaze most often and longest at areas that conveyed most social information, such as the eye region of the face (T1), and social images (T3). Participants gazed most often and longest at happy faces (T2) in still images, and more often and longer at the facial area in negative than in positive video clips (T4). No differences occurred between lonely and nonlonely participants in their gazing times and frequencies, nor at first fixations at social cues in the four different tasks. Based on this study, we found no evidence that overt visual attention to social cues differs between lonely and nonlonely individuals. This implies that biases in social information processing of lonely individuals may be limited to other phases of social information processing. Alternatively, biased overt attention to social cues may only occur under specific conditions, for specific stimuli or for specific lonely individuals.     

Modifying the object-choice task: Is the way you look important for ravens?

Most animals seem to have difficulties in using gaze cues to find hidden food in object-choice tasks. For instance, chimpanzees usually fail in these tests, even though they are capable of following other's gaze geometrically behind barriers. Similar to chimpanzees, common ravens are skilled in tracking other's gaze but fail in object-choice tasks. We here explored whether procedural modifications, which had been used successfully in chimpanzees, would also yield positive results in ravens. In our modifications (a) the experimenter approached the cup while gazing at it, (b) the gaze cue was accompanied by a sound and (c) the experimenter could actually see the food while giving the gaze cue. Two out of seven birds performed above chance level in some of these conditions. However, we ascribe this improvement to the individuals' learning ability rather than to an understanding of the communicative nature of the task. This interpretation is further supported by results of a follow-up experiment suggesting that ravens may not rely on conspecifics' gaze cues for finding food caches in a natural foraging context. In sum, our results suggest that ravens may not transfer their gaze follow abilities to foraging situations involving hidden food.     

Development of gaze following abilities in wolves (Canis lupus)

The ability to coordinate with others' head and eye orientation to look in the same direction is considered a key step towards an understanding of others mental states like attention and intention. Here, we investigated the ontogeny and habituation patterns of gaze following into distant space and behind barriers in nine hand-raised wolves. We found that these wolves could use conspecific as well as human gaze cues even in the barrier task, which is thought to be more cognitively advanced than gazing into distant space. Moreover, while gaze following into distant space was already present at the age of 14 weeks and subjects did not habituate to repeated cues, gazing around a barrier developed considerably later and animals quickly habituated, supporting the hypothesis that different cognitive mechanisms may underlie the two gaze following modalities. More importantly, this study demonstrated that following another individuals' gaze around a barrier is not restricted to primates and corvids but is also present in canines, with remarkable between-group similarities in the ontogeny of this behaviour. This sheds new light on the evolutionary origins of and selective pressures on gaze following abilities as well as on the sensitivity of domestic dogs towards human communicative cues.     

Point Me in the Right Direction: Same and Cross Category Visual Aftereffects to Directional Cues

Of the many hand gestures that we use in communication pointing is one of the most common and powerful in its role as a visual referent that directs joint attention. While numerous studies have examined the developmental trajectory of pointing production and comprehension, very little consideration has been given to adult visual perception of hand pointing gestures. Across two studies, we use a visual adaptation paradigm to explore the mechanisms underlying the perception of proto-declarative hand pointing. Twenty eight participants judged whether 3D modeled hands pointed, in depth, at or to the left or right of a target (test angles of 0°, 0.75° and 1.5° left and right) before and after adapting to either hands or arrows which pointed 10° to the right or left of the target. After adaptation, the perception of the pointing direction of the test hands shifted with respect to the adapted direction, revealing separate mechanisms for coding right and leftward pointing directions. While there were subtle yet significant differences in the strength of adaptation to hands and arrows, both cues gave rise to a similar pattern of aftereffects. The considerable cross category adaptation found when arrows were used as adapting stimuli and the asymmetry in aftereffects to left and right hands suggests that the adaptation aftereffects are likely driven by simple orientation cues, inherent in the morphological structure of the hand, and not dependent on the biological status of the hand pointing cue. This finding provides evidence in support of a common neural mechanism that processes these directional social cues, a mechanism that may be blind to the biological status of the stimulus category.     

The antigen-antibody interaction algebraically interpreted as a relational process.

The antigen-antibody interaction occurring previous to the triggering of the immunological response is analyzed as a relational process in terms of lattices. Accordingly, this process is expressed as a lattice belonging to a pseudo-Boolean algebraic variety. The Heyting arrow operation, which appears in this kind of algebra, is used to analyze behaviors between non-comparable biological states expressed by the lattice. The resulting states coming from the arrows are connected with the influence of increasing and decreasing energies involved in the linking process.     

Beetle and plant arrow poisons of the Ju|’hoan and Hai||om San peoples of Namibia (Insecta,Coleoptera, Chrysomelidae; Plantae,Anacardiaceae, Apocynaceae,Burseraceae)

The use of archery to hunt appears relatively late in human history. It is poorly understood but the application of poisons to arrows to increase lethality must have occurred shortly after developing bow hunting methods; these early multi-stage transitions represent cognitive shifts in human evolution. This paper is a synthesis of widely-scattered literature in anthropology, entomology, and chemistry, dealing with San (“Bushmen”) arrow poisons. The term San (or Khoisan) covers many indigenous groups using so-called ‘click languages’ in southern Africa. Beetles are used for arrow poison by at least eight San groups and one non-San group. Fieldwork and interviews with Ju|’hoan and Hai||om hunters in Namibia revealed major differences in the nature and preparation of arrow poisons, bow and arrow construction, and poison antidote. Ju|’hoan hunters use leaf-beetle larvae of Diamphidia Gerstaecker and Polyclada Chevrolat (Chrysomelidae: Galerucinae: Alticini) collected from soil around the host plants Commiphora africana (A. Rich.) Engl. and Commiphora angolensis Engl. (Burseracaeae). In the Nyae Nyae area of Namibia, Ju|’hoan hunters use larvae of Diamphidia nigroornata Ståhl. Larvae and adults live above-ground on the plants and eat leaves, but the San collect the underground cocoons to extract the mature larvae. Larval hemolymph is mixed with saliva and applied to arrows. Hai||om hunters boil the milky plant sap of Adenium bohemianum Schinz (Apocynaceae) to reduce it to a thick paste that is applied to their arrows. The socio-cultural, historical, and ecological contexts of the various San groups may determine differences in the sources and preparation of poisons, bow and arrow technology, hunting behaviors, poison potency, and perhaps antidotes.     

Full pattern of transient apical ballooning of the left ventricle triggered by minor myocardial infarction

A 60-year-old female with a history of hypertension, hypercholesterolaemia, and diabetes mellitus presented two hours after sudden onset of severe persistent chest pain. Electrocardiography showed ST-segment elevation in the inferolateral leads (figure 1A). Coronary angiography revealed a subtotal occlusion of a small left marginal side branch (figure 1B; arrow) and a normal right coronary artery, which could not explain the full typical pattern of apical ballooning as demonstrated by left ventricular angiography (figure 1C and D; arrows).     

Monkeys head-gaze following is fast,precise and not fully suppressible

Human eye-gaze is a powerful stimulus, drawing the observer''s attention to places and objects of interest to someone else (‘eye-gaze following’). The largely homogeneous eyes of monkeys, compromising the assessment of eye-gaze by conspecifics from larger distances, explain the absence of comparable eye-gaze following in these animals. Yet, monkeys are able to use peer head orientation to shift attention (‘head-gaze following’). How similar are monkeys'' head-gaze and human eye-gaze following? To address this question, we trained rhesus monkeys to make saccades to targets, either identified by the head-gaze of demonstrator monkeys or, alternatively, identified by learned associations between the demonstrators'' facial identities and the targets (gaze versus identity following). In a variant of this task that occurred at random, the instruction to follow head-gaze or identity was replaced in the course of a trial by the new rule to detect a change of luminance of one of the saccade targets. Although this change-of-rule rendered the demonstrator portraits irrelevant, they nevertheless influenced performance, reflecting a precise redistribution of spatial attention. The specific features depended on whether the initial rule was head-gaze or identity following: head-gaze caused an insuppressible shift of attention to the target gazed at by the demonstrator, whereas identity matching prompted much later shifts of attention, however, only if the initial rule had been identity following. Furthermore, shifts of attention prompted by head-gaze were spatially precise. Automaticity and swiftness, spatial precision and limited executive control characterizing monkeys'' head-gaze following are key features of human eye-gaze following. This similarity supports the notion that both may rely on the same conserved neural circuitry.     

Either or neither, but not both: locating the effects of masked primes

Execution of a response that has been primed by a backward-masked stimulus is inhibited (negative compatibility effect; NCE). Three experiments investigated the locus of this inhibition. Masked primes (left- or right-pointing arrows) were followed either by an arrow or a circle target. Arrow targets always required a left- or right-hand response, but the experiments differed in the response required to circles: press neither, either or both response keys (i.e. nogo, free choice and bimanual, respectively). Arrow targets showed the usual NCEs. Circle targets showed NCEs in the form of a response bias away from the primed response in the nogo and free-choice tasks; primes and targets differed on these trials, ruling out a perceptual explanation of the NCE. The bimanual task showed no such bias, suggesting that the NCE is located at a level of abstract response codes rather than specific muscle commands.     

Spatial code interference on directional responses.

The interference from an irrelevant position cue was compared in a reaction-time paradigm using voice and manual responses. The subjects were required to say 'left' or 'right' or to press left or right keys in response to arrow directions, and the arrows were presented at left or right side display positions irrelevant to the task. Display position significantly increased latency when it did not match the response to the relevant direction cue for both spatial (key-press) and non-spatial (voice) responses (73 and 59 ms, respectively). When presented alone, the position cue was processed faster than the direction cue for both manual and verbal responses. Results are discussed in terms of a common abstract mediator for left-right responses between modes and the processing speed difference between the relevant and irrelevant cue. The irrelevant left-right position code may occupy some limited-capacity channel ahead of the left-right code derived from processing the relevant direction cue.     

Sound-localization experiments with barn owls in virtual space: influence of broadband interaural level difference on head-turning behavior

Interaural level differences play an important role for elevational sound localization in barn owls. The changes of this cue with sound location are complex and frequency dependent. We exploited the opportunities offered by the virtual space technique to investigate the behavioral relevance of the overall interaural level difference by fixing this parameter in virtual stimuli to a constant value or introducing additional broadband level differences to normal virtual stimuli. Frequency-specific monaural cues in the stimuli were not manipulated. We observed an influence of the broadband interaural level differences on elevational, but not on azimuthal sound localization. Since results obtained with our manipulations explained only part of the variance in elevational turning angle, we conclude that frequency-specific cues are also important. The behavioral consequences of changes of the overall interaural level difference in a virtual sound depended on the combined interaural time difference contained in the stimulus, indicating an indirect influence of temporal cues on elevational sound localization as well. Thus, elevational sound localization is influenced by a combination of many spatial cues including frequency-dependent and temporal features.     

Specificity changes in the evolution of type II restriction endonucleases: a biochemical and bioinformatic analysis of restriction enzymes that recognize unrelated sequences

How restriction enzymes with their different specificities and mode of cleavage evolved has been a long standing question in evolutionary biology. We have recently shown that several Type II restriction endonucleases, namely SsoII (downward arrow CCNGG), PspGI (downward arrow CCWGG), Eco-RII (downward arrow CCWGG), NgoMIV (G downward arrow CCGGC), and Cfr10I (R downward arrow CCGGY), which recognize similar DNA sequences (as indicated, where the downward arrows denote cleavage position), share limited sequence similarity over an interrupted stretch of approximately 70 amino acid residues with MboI, a Type II restriction endonuclease from Moraxella bovis (Pingoud, V., Conzelmann, C., Kinzebach, S., Sudina, A., Metelev, V., Kubareva, E., Bujnicki, J. M., Lurz, R., Luder, G., Xu, S. Y., and Pingoud, A. (2003) J. Mol. Biol. 329, 913-929). Nevertheless, MboI has a dissimilar DNA specificity (downward arrow GATC) compared with these enzymes. In this study, we characterize MboI in detail to determine whether it utilizes a mechanism of DNA recognition similar to SsoII, PspGI, EcoRII, NgoMIV, and Cfr10I. Mutational analyses and photocross-linking experiments demonstrate that MboI exploits the stretch of approximately 70 amino acids for DNA recognition and cleavage. It is therefore likely that MboI shares a common evolutionary origin with SsoII, PspGI, EcoRII, NgoMIV, and Cfr10I. This is the first example of a relatively close evolutionary link between Type II restriction enzymes of widely different specificities.