The weight of expectation: Implicit, rather than explicit, prior expectations drive the size-weight illusion

In the size-weight illusion, small objects feel heavier than identically weighted larger objects. This illusion is thought to be a consequence of how one's prior expectations can influence conscious perception--lifters expect the large object to outweigh the small object and subsequently experience it as feeling lighter than they expected it to be. Here, we directly examined how a familiar object's identity can affect how heavy someone expects it to be, and how these expectations will influence subsequent perceptions of heaviness. We describe two novel weight illusions induced with familiar objects. In one condition, participants judged the weight of a set of similar-size objects with very different natural weights (a polystyrene sphere, a tennis ball, and a cricket ball), which had all been adjusted to weigh the same amount as one another. In this condition, participants experienced a small, but reliable, weight illusion, with the lightest looking ball feeling heavier than the heaviest looking ball. In the other condition, participants judged the weights of a different set of balls, which were different sizes, but similar natural weights, to one another (a golf ball, a foam soccer ball, and an inflated beach ball). Again, participants experienced a perceptual illusion, but in the opposite direction. Surprisingly, participant's perceptions matched, rather than contrasted with, their explicit expectations such that, even though they expected the golf ball to outweigh the beach ball they perceived the golf ball as feeling heavier than the beach ball. The effect of object mass appeared to dominate the effect of conscious expectations, suggesting that contrasting expectations of heaviness are not necessary to experience weight illusions and that current models of this robust perceptual effect must be revised.

Identifying and counting objects: The role of sortal concepts

Sortal terms, such as table or horse, are nouns akin to basic-level terms. According to some theories, the meaning of sortals provides conditions for telling objects apart (individuating objects, e.g., telling one table from a second) and for identifying objects over time (e.g., determining that a particular table at one time is the same table at another). A number of psychologists have proposed that sortal concepts likewise provide psychologically real conditions for individuating and identifying things. However, this paper reports five experiments that cast doubt on these psychological claims. Experiments 1-3 suggest that sortal concepts do not determine when an object ceases to exist and therefore do not decide when the object can no longer be identical to a later one. Experiments4-5 similarly suggest that sortal concepts do not provide determinate conditions for individuating objects. For example, they do not always decide whether a room contains one table or two. All five experiments feature ordinary objects undergoing ordinary changes.

Computational model of visual hallucination in dementia with Lewy bodies

Patients with dementia with Lewy bodies (DLB) frequently experience visual hallucination (VH), which has been aptly described as people seeing things that are not there. The distinctive character of VH in DLB necessitates a new theory of visual cognition. We have conducted a series of studies with the aim to understand the mechanism of this dysfunction of the cognitive system. We have proposed that if we view the disease from the internal mechanism of neurocognitive processes, and if also take into consideration recent experimental data on conduction abnormality, at least some of the symptoms can be understood within the framework of network (or disconnection) syndromes. This paper describes the problem from a computational aspect and tries to determine whether conduction disturbances in a computational model can in fact produce a "computational" hallucination under appropriate assumptions.

The influence of object identity on obstacle avoidance reaching behaviour

When reaching for target objects, we hardly ever collide with other objects located in our working environment. Behavioural studies have demonstrated that the introduction of non-target objects into the workspace alters both spatial and temporal parameters of reaching trajectories. Previous studies have shown the influence of spatial object features (e.g. size and position) on obstacle avoidance movements. However, obstacle identity may also play a role in the preparation of avoidance responses as this allows prediction of possible negative consequences of collision based on recognition of the obstacle. In this study we test this hypothesis by asking participants to reach towards a target as quickly as possible, in the presence of an empty or full glass of water placed about half way between the target and the starting position, at 8 cm either left or right of the virtual midline. While the spatial features of full and empty glasses of water are the same, the consequences of collision are clearly different. Indeed, when there was a high chance of collision, reaching trajectories veered away more from filled than from empty glasses. This shows that the identity of potential obstacles, which allows for estimating the predicted consequences of collision, is taken into account during obstacle avoidance.