Effects of Acute Stress or Centrally Injected Interleukin-1beta on Neuropeptide Expression in the Immune System

Acute stress stimulates the expression and release of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) from the hypothalamus, and the pro-opiomelanocortin products beta-endorphin and ACTH from the anterior pituitary. These neuropeptides are also expressed in immune tissues, and it has been proposed that they may modulate immune responses to stress through paracrine mechanisms. We subjected rats to restraint stress or central injection of interleukin (IL)-1beta to determine whether these acute stimuli can alter the expression of neuropeptides in the spleen and thymus. Restraint stress significantly increased the contents of all these neuropeptides in thymic, but not splenic, extracts. A single icv injection of IL-1beta increased contents of CRH, AVP, ACTH and beta-endorphin in the spleens of both sham-operated and adrenalectomised (ADX) rats. IL-1beta increased thymic contents of CRH and ACTH in sham-operated rats but these increases were not observed in ADX rats. These results suggest that the effects of IL-1beta on neuropeptide expression in the spleen are independent of glucocorticoids, whereas IL-1beta stimulation of neuropeptide expression in the thymus is dependent on circulating glucocorticoids. There were significant correlations between increases in CRH, ACTH and beta-endorphin in the spleen, and between CRH and ACTH in the thymus, consistent with the suggestion that IL-1beta-induced increases in ACTH and beta-endorphin may be mediated through CRH. These results provide evidence that stressors can directly influence neuropeptide expression in immune tissues. Thus stress may influence immune functions through paracrine mechanisms involving locally synthesised neuropeptides as well as through activation of the hypothalamo-pituitary-adrenal axis.     

Enumeration of small collections violates Weber’s law

In a phenomenon called subitizing, we can immediately generate exact counts of small collections (one to three objects), in contrast to larger collections, for which we must either create rough estimates or serially count. A parsimonious explanation for this advantage for small collections is that noisy representations of small collections are more tolerable, due to the larger relative differences between consecutive numbers (e.g., 2 vs. 3 is a 50 % increase, but 10 vs. 11 is only a 10 % increase). In contrast, the advantage could stem from the fact that small-collection enumeration is more precise, relying on a unique mechanism. Here, we present two experiments that conclusively showed that the enumeration of small collections is indeed “superprecise.” Participants compared numerosity within either small or large visual collections in conditions in which the relative differences were controlled (e.g., performance for 2 vs. 3 was compared with performance for 20 vs. 30). Small-number comparison was still faster and more accurate, across both “more–fewer” judgments (Exp. 1), and “same–different” judgments (Exp. 2). We then reviewed the remaining potential mechanisms that might underlie this superprecision for small collections, including the greater diagnostic value of visual features that correlate with number and a limited capacity for visually individuating objects.     

Anxious mood narrows attention in feature space

Spatial attention can operate like a spotlight whose scope can vary depending on task demands. Emotional states contribute to the spatial extent of attentional selection, with the spotlight focused more narrowly during anxious moods and more broadly during happy moods. In addition to visual space, attention can also operate over features, and we show here that mood states may also influence attentional scope in feature space. After anxious or happy mood inductions, participants focused their attention to identify a central target while ignoring flanking items. Flankers were sometimes coloured differently than targets, so focusing attention on target colour should lead to relatively less interference. Compared to happy and neutral moods, when anxious, participants showed reduced interference when colour isolated targets from flankers, but showed more interference when flankers and targets were the same colour. This pattern reveals that the anxious mood caused these individuals to attend to the irrelevant feature in both cases, regardless of its benefit or detriment. In contrast, participants showed no effect of colour on interference when happy, suggesting that positive mood did not influence attention in feature space. These mood effects on feature-based attention provide a theoretical bridge between previous findings concerning spatial and conceptual attention.     

Similarity grouping as feature-based selection

Our visual system groups objects with similar features, such as colour, orientation, or shape. We argue that similarity grouping is nothing more than global selection of a certain feature value, such as red, horizontal, or circular. This account makes the striking prediction that only one feature group can be created at a time. Here we provide the most direct evidence yet for this proposal, using a number estimation task that forces simultaneous processing of all objects. Multiple similarity cues failed to produce grouping in this task, in contrast to proximity, connectivity, and common region, which all showed strong grouping effects.     

Characteristic sounds make you look at target objects more quickly

When you are looking for an object, does hearing its characteristic sound make you find it more quickly? Our recent results supported this possibility by demonstrating that when a cat target, for example, was presented among other objects, a simultaneously presented “meow” sound (containing no spatial information) reduced the manual response time for visual localization of the target. To extend these results, we determined how rapidly an object-specific auditory signal can facilitate target detection in visual search. On each trial, participants fixated a specified target object as quickly as possible. The target’s characteristic sound speeded the saccadic search time within 215–220 msec and also guided the initial saccade toward the target, compared with presentation of a distractor’s sound or with no sound. These results suggest that object-based auditory—visual interactions rapidly increase the target object’s salience in visual search.     

Number estimation relies on a set of segmented objects

How do we estimate the number of objects in a set? Two types of visual representations might underlie this ability - an unsegmented visual image or a segmented collection of discrete objects. We manipulated whether individual objects were isolated from each other or grouped into pairs by irrelevant lines. If number estimation operates over an unsegmented image, then this manipulation should not affect estimates. But if number estimation relies on a segmented image, then grouping pairs of objects into single units should lead to lower estimates. In Experiment 1 participants underestimated the number of grouped objects, relative to disconnected objects in which the connecting lines were ‘broken’. Experiment 2 presents evidence that this segmentation process occurred broadly across the entire set of objects. In Experiment 3, a staircase procedure provides a quantitative measure of the underestimation effect. Experiment 4 shows that the strength of the grouping effect was equally strong for a single thin line, and the effect can be eliminated by a small break in the line. These results provide direct evidence that number estimation relies on a segmented input.     

Flexible visual processing of spatial relationships

Visual processing breaks the world into parts and objects, allowing us not only to examine the pieces individually, but also to perceive the relationships among them. There is work exploring how we perceive spatial relationships within structures with existing representations, such as faces, common objects, or prototypical scenes. But strikingly, there is little work on the perceptual mechanisms that allow us to flexibly represent arbitrary spatial relationships, e.g., between objects in a novel room, or the elements within a map, graph or diagram. We describe two classes of mechanism that might allow such judgments. In the simultaneous class, both objects are selected concurrently. In contrast, we propose a sequential class, where objects are selected individually over time. We argue that this latter mechanism is more plausible even though it violates our intuitions. We demonstrate that shifts of selection do occur during spatial relationship judgments that feel simultaneous, by tracking selection with an electrophysiological correlate. We speculate that static structure across space may be encoded as a dynamic sequence across time. Flexible visual spatial relationship processing may serve as a case study of more general visual relation processing beyond space, to other dimensions such as size or numerosity.     

A simple proximity heuristic allows tracking of multiple objects through occlusion

Moving objects in the world present a challenge to the visual system, in that they often move in and out of view as they are occluded by other surfaces. Nevertheless, the ability to track multiple objects through periods of occlusion is surprisingly robust. Here, we identify a simple heuristic that underlies this ability: Pre- and postocclusion views of objects are linked together solely by their spatial proximity. Tracking through occlusion was always improved when the postocclusion instances reappeared closer to the preocclusion views. Strikingly, this was true even when objects?? previous trajectories predicted different reappearance locations and when objects reappeared ??too close,?? from invisible ??slits?? in empty space, rather than from more distant occluder contours. Tracking through occlusion appears to rely only on spatial proximity, and not on encoding heading information, likely reappearance locations, or the visible structure of occluders.     

Objects with reduced visibility still contribute to size averaging

People can rapidly judge the average size of a collection of objects with considerable accuracy. In this study, we tested whether this size-averaging process relies on relatively early object representations or on later object representations that have undergone iterative processing. We asked participants to judge the average size of a set of circles and, in some conditions, presented two additional circles that were either smaller or larger than the average. The additional circles were surrounded by four-dot masks that either lingered longer than the circle array, preventing further processing with object substitution masking (OSM), or disappeared simultaneously with the circle array, allowing the circle representation to reach later visual processing stages. Surprisingly, estimation of average circle size was modulated by both visible circles and circles whose visibility was impaired by OSM. There was also no correlation across participants between the influence of the masked circles and susceptibility to OSM. These findings suggest that relatively early representations of objects can contribute to the size-averaging process despite their reduced visibility.