How can we learn what attention is? Response gating via multiple direct routes kept in check by inhibitory control processes

To explore the time course of space- and object-based attentional selection processes I analysed the shapes of the response time (RT) and accuracy distributions of left/right arrow identification responses in the two-rectangle paradigm. After cueing one of the four ends of two horizontally or vertically oriented rectangles the arrow typically appears at the cued location (valid), or sometimes at an uncued location in the same (invalid-same) or other rectangle (invalid-different). The data point to a multiple-route model in which (a) an informative cue generates response channel activation before arrow signals emerge, (b) the task-irrelevant arrow location is represented in multiple egocentric and allocentric reference frames around 150 ms after target onset, with the former including a reference frame centered on the currently attended location, (c) the task-irrelevant spatial codes activate premature response tendencies that are actively inhibited to allow gating of arrow direction signals, (d) after an invalid cue the onset of the arrow triggers an “attention shift” – acting between 150 and 240 ms after target onset – that strongly interferes with task performance in certain conditions (invalid-same cueing with horizontal rectangles, and invalid-different cueing with vertical rectangles), and (e) participants differ in which task-irrelevant codes they preferentially inhibit. These results pave the way for future confirmatory studies to temporally characterize and disentangle the contributions of different types of response channel activation processes, from those of reactive cognitive control processes including active and selective response suppression.

Premature commitment to uncertain beliefs during human NMDA receptor hypofunction

In uncertain environments, accurate decision-making requires integrating ambiguous or conflicting signals – a cognitive inference process thought to require n-methyl-d-aspartate (NMDA) synaptic receptors. Here we characterized the causal impact of human NMDA receptor hypofunction on cognitive inference using placebo-controlled infusions of ketamine in a visual cue combination task. Participants tested under ketamine showed elevated uncertainty, together with impaired cognitive inference despite intact visual processing. This behavioral effect of ketamine was associated in patterns of electrical brain activity with degraded and unbalanced coding of presented cues in associative cortex, followed by premature response preparation in motor cortex. Through quantitative simulations, we propose that these cognitive alterations reflect an urge to explain away the elevated uncertainty triggered by ketamine. This compensatory mechanism may cause the emergence of psychotic symptoms observed under chronic NMDA receptor dysfunction, but also forge unusually strong beliefs when confronted with uncertainty in everyday life.

The Psychological Factors of a Premature Response Based on Contingent Negative Variation

The psychological factors of a premature response on simple reaction-time tasks were examined by comparing the difference between control responses (33 samples) and premature responses (33 samples) using the index of Contingent Negative Variation (CNV). The first (warning) stimulus was a click, the second (imperative) stimulus was a colored circular figure presented on a CRT, and the interstimulus interval was set at 3 sec. 72 trials were administered to the 24 subjects, then 33 artifact-free CNV data in a premature response were shown. Analyses indicated that CNV amplitudes in the premature response were lower than those in the control response at frontal position. Especially in the premature response, CNV waveforms stayed around baseline toward S2 at F3 and F4. In the analyses of variance, every CNV component (early, late, and whole components) at F4 or Fz was significantly lower for the premature response. These results suggested that the optimal prediction, arousal, and attention do not seem to be maintained in a premature response.

Effects of moderate hypoxia on premature action potentials of rabbit papillary muscle

Experiments were performed to study the effects of hypoxia on the characteristics of premature action potentials of rabbit papillary muscles. At normal resting potential, the duration of the premature action potential at the shortest coupling intervals was always greater than that of the control response. As the coupling interval was increased beyond 150 ms, the duration of the premature action potential regained control values. In cells depolarized to −70 mV by KCl, early lengthening of the premature response was attenuated. After 60 min of hypoxia, recovery of action potential duration at normal and reduced resting potentials was accelerated. The maximum rate of depolarization and its reactivation time constant were not affected by 60 min of hypoxia. It is suggested that intracellular free Ca is important in the control of action potential duration via the outward background potassium current.

Supernormal conduction in the canine bundle of His and proximal bundle branches

We used close bipolar intramural electrodes and catheter electrodes to study the characteristics of conduction in the bundle of His and proximal bundle branches during premature atrial beats in 17 open-chest anesthetized dogs. The electrophysiological properties of the proximal conducting system were heterogenous. The shortest interval between a normal His bundle response and a premature response that was not accompanied by changes in conduction time (the total recovery time) was 258.8 +/- 23.9 (SD) ms for the proximal His and 310.7 +/- 30.6 ms for the distal His and proximal bundle branches. A period of supernormal conduction, in which the conduction times of premature beats were faster than during earlier or later beats, was localized to the distal portion of the bundle of His and proximal bundle branches. The minimal conduction time during the supernormal period was decreased by 9.6 +/- 4.6% below control diastolic conduction times, and the supernormal period was 61.0 +/- 25.7 ms in duration. The characteristics of the period of supernormal conduction in the distal bundle of His and proximal bundle branches were very similar to those previously found in the peripheral bundle branch-Purkinje system. The mechanism of supernormal conduction in the bundle of His is most probably due to a period of supernormal excitability.

The Reproductive Behaviour and the Nature of Sexual Selection in Scatophaga Stercoraria L. (Diptera : Scatophagidae)

Sexual attractiveness of calypterate Diptera may be measured by their ability to elicit encounters from individuals of opposite sex. Stationary female S. stercoraria elicit a much higher encounter rate from searching males than do stationary males and immobile pairs elicit an intermediate rate. It is therefore concluded that males can 'recognise' these three types of individual; probably by visual means. Sexual attractiveness after contact may be measured by the extent to which a contact courtship bout progresses or by measuring the 'bout duration'. There is no difference between the bout durations of males with other males and that with pairs. This implies that on contact there is no ability to discriminate between pairs and males. This is not true, however, when an attacking male manages to touch a paired female during a contact bout. This results in a struggle between males for the possession of the female. Paired males perform characteristic rejection response patterns to different types of encounter bout, depending on the direction of attack and the extent to which the bout proceeds. The responses appear to have evolved to prevent touching of the female by the attacker. By far the most common type of bout occurs when the attacker mounts a pair. The paired male almost always reponds by raising both middle legs and 'standing' (straightening the front legs), a reaction which doubles the distance between the attacker and the female and thus effectively prevents contact of the attacker with the female. This is essentially a contact reaction, since a premature response would allow direct access to the female rather than having the effect of 'shrugging off' the attacker. The rejection reactions of paired males could have arisen from the avoidance reactions of single males. Single ('searching') males perform most of the reactions of paired males but less vigorously, and in addition perform swaying movements similar to those of females. The avoidance reactions of single males may have adaptive value in reducing the time wasted in a bout with another male. With both single and paired males, the intensity of the rejection response elicited is proportional to the extent to which the bout proceeds after contact. Males in the passive phase (i.e. paired to ovipositing females) react most intensely to a given type of bout. Struggles occur in about 7% of encounters with both type of pair and result from failure of the rejection responses, instability, or multiple attacks. They involve up to several minutes time waste before one male finally dominates. Take-overs (where the original male is ousted) are much more frequent in attacks of pairs involved in oviposition than with pairs in genital contact, occurring in 1.75% and 0.65% of encounters respectively. The second male then begins genital contact immediately.