How many variables can humans process?

The conceptual complexity of problems was manipulated to probe the limits of human information processing capacity. Participants were asked to interpret graphically displayed statistical interactions. In such problems, all independent variables need to be considered together, so that decomposition into smaller subtasks is constrained, and thus the order of the interaction directly determines conceptual complexity. As the order of the interaction increases, the number of variables increases. Results showed a significant decline in accuracy and speed of solution from three-way to four-way interactions. Furthermore, performance on a five-way interaction was at chance level. These findings suggest that a structure defined on four variables is at the limit of human processing capacity.     

How many parameters can a model have and still be testable?

A standard rule of thumb states that a model has too many parameters to be testable if and only if it has at least as many parameters as empirically observable quantities. We argue that when one asks whether a model has too many parameters to be testable, one implicitly refers to a particular type of testability, which we call quantitative testability. A model is defined to be quantitatively testable if the model's predictions have zero probability of being correct by chance. Next, we propose a new rule of thumb, based on the rank of the Jacobian matrix of a model (i.e., the matrix of partial derivatives of the function that maps the model's parameter values onto predicted experimental outcomes). According to this rule, a model is quantitatively testable if and only if the rank of the Jacobian matrix is less than the number of observables. (The rank of his matrix can be found with standard computer algorithms.) Using Sard's theorem, we prove that the proposed new rule of thumb is correct provided that certain “smoothness” conditions are satisfied. We also discuss the relation between quantitative testability and reparameterization, identifiability, and goodness-of-fit testing.     

How many kinds of consciousness?

Ned Block's influential distinction between phenomenal and access consciousness has become a staple of current discussions of consciousness. It is not often noted, however, that his distinction tacitly embodies unargued theoretical assumptions that favor some theoretical treatments at the expense of others. This is equally so for his less widely discussed distinction between phenomenal consciousness and what he calls reflexive consciousness. I argue that the distinction between phenomenal and access consciousness, as Block draws it, is untenable. Though mental states that have qualitative character plainly differ from those with no mental qualities, a mental state's being conscious is the same property for both kinds of mental state. For one thing, as Block describes access consciousness, that notion does not pick out any property that we intuitively count as a mental state's being conscious. But the deeper problem is that Block's notion of phenomenal consciousness, or phenomenality, is ambiguous as between two very different mental properties. The failure to distinguish these results in the begging of important theoretical questions. Once the two kinds of phenomenality have been distinguished, the way is clear to explain qualitative consciousness by appeal to a model such as the higher-order-thought hypothesis.     

How many locations can be selected at once?

The visual system uses several tools to select only the most relevant visual information for further processing, including selection by location. In the present study, the authors explored how many locations can be selected at once. Although past evidence from several visual tasks suggests that the visual system can operate on a fixed number of 4 objects or locations at once, the authors found that this capacity varies widely in response to the precision of selection required by the task. When the authors required precise selection regions, only 2-3 locations could be selected. But when the selection regions could be coarser, up to 6-7 locations could be selected. The authors discuss potential mechanisms underlying the selection of multiple locations and review the evidence for fixed limits in visual attention.     

How many notions of necessity?

Evans distinguishes between superficial necessity and deep necessity in his analysis of the contingent a priori. The distinction between these two notions of necessity is formalized by Davies and Humberstone through the addition of the operator Fixedly to Actuality Modal Logic (AML, S5A), where deep necessity is represented by the combination Fixedly Actually. Wehmeier’s Subjunctive Modal Logic (SML) provides an extension of the expressive capacity of ordinary modal predicate logic alternative to AML. I add Fixedly to SML and show that in the system SML with Fixedly the distinction between deep and superficial necessity disappears. I conclude that the existence of the distinction between deep and superficial necessity, as well as the existence of the contingent a priori, cannot be asserted independently of the choice of background logic.     

The perceived effectiveness of road safety interventions: Regulation of drivers’ behavioral intentions and self-consciousness

We consider road safety interventions to be potential sources of social influence, altering the intentions and behaviors of drivers when they are perceived by the latter as effective. We also consider that perceiving their effectiveness depends on drivers’ self-consciousness. 852 drivers replied to a questionnaire measuring dispositional self-consciousness, the perception of the effectiveness of 10 road safety interventions, and reported intentions and behaviors related to speeding and drinking and driving. The results revealed several phenomena: (1) interventions were perceived as related to penalty/surveillance or social communication (factor analysis); (2) the former were perceived as more effective than the latter; (3) the perceived effectiveness of road safety interventions was moderately correlated with intentions and behaviors; (4) this link was stronger for interventions of the penalty/surveillance type; (5) age, level of education, frequency of use of a vehicle and gender were moderately associated with the perception of these interventions; (6) self-consciousness (in particular its public dimension) had an additional positive association with this perceived effectiveness. These results are discussed from a practical and methodological point of view.     

Combining the judgments of experts: How many and which ones?

R. M. Hogarth (1978, Organizational Behavior and Human Performance, 21, 40–46) presents an analytical model which, under certain conditions, may be useful for estimating both the number of experts to include in a staticized group and which experts. This paper reports a study of an important real-world judgment task used to evaluate (1) the extent to which the specified conditions hold and (2) the effect of violations of the conditions on the ability of the model to approximate the actual empirical validities that result from forming such groups. The results indicate that, although the specified conditions hold only moderately well, the model suggested by Hogarth provides a remarkably good approximation to the actual empirical validities of the staticized groups.     

The suffix effect: How many positions are involved?

Three experiments tested the effect of the availability of the last item on the recall performance for earlier list items in a stimulus suffix paradigm. A decrement due to the suffix occurred for preterminal positions even when the last item was made available. This preterminal suffix effect was found to be more extensive in a condition in which subjects were free to recall the end items first than in a condition in which subjects were forced to recall in a strict left-to-right fashion.     

How many faces can be processed during a single eye fixation?

The purpose of our study was to estimate the perceptual span for facial information: how many faces can be processed during a single eye fixation. We used a visual-search task, in which the targets and distractors were facial photographs. The task of the observer was to search for and identify a target face in an array of faces. We measured the time needed for one search--threshold search time--by using a multiple-alternative staircase method. The threshold represents the duration of stimulus presentation at which the probability of correct responses was 79%. The array size was varied from 2 x 2 to 8 x 8 faces. Simultaneously with the performance measurements we measured eye movements with a video eye tracker. We found that threshold search time increased with increasing set size nearly linearly. The number of fixations also increased linearly from unity at the smallest set size to about fifteen at the largest set size. The result of 2 x 2 faces during a single fixation gave an estimate of 4 faces for the perceptual span. If, on average, only half of the elements had to be scanned for finding the target, 15 fixations at the largest set size (8 x 8) gave another estimate of 2.13 faces. The mean fixation duration was around 200 ms. Thus, the results suggest that 2-4 faces can be processed during one fixation of about 200 ms.     

How can we improve safety culture in transport organizations? A review of interventions,effects and influencing factors

The main objectives of the present study are to (a) map interventions that can be used to develop good safety culture in transport companies within road, sea, air and rail transport, (b) assess expected effects of interventions on safety culture and safety outcomes and (c) identify factors influencing safety culture change. By systematically reviewing the scientific literature, we identify 20 studies that describe and evaluate interventions to improve safety culture in road, rail, sea and air transport organizations. The review is reported according to PRISMA guidelines. The interventions studied vary widely in their comprehensiveness, but a lack of both standardized outcome measures and controlled evaluations means that it is difficult to compare different interventions, either within or across sectors. Most studies, however, report improvements in safety culture where this is measured. We find that attempts to understand the mechanisms of cultural change leading to behavioural change and improved safety performance are lacking. Although safety culture is an organizational measure, we only found one peer-reviewed study of an attempt to improve safety culture in a single air transport organization and no studies of this in the maritime sector. We conclude that on the whole the reviewed safety culture interventions seem to be effective, but comprehensive and resource demanding. We suggest that future research should develop simpler interventions by focusing on the basic requirements of safety culture change. We contribute to this by identifying four key activities (content) which seem to be common in all the reviewed interventions, and eight key factors (process) influencing the success of efforts to influence safety culture. The basic requirements of safety culture change seem to be to institutionalize joint discussions of work place hazards facilitated by manager commitment and employee involvement.     

Cyber-Islamophobia? The case of WikiIslam

A large amount of academic research has analysed and documented the fact that Muslims are often presented in a negative or stereotypical way in Western media and popular culture. This article focuses on how the Internet can also be used in spreading and publishing anti-Islamic and anti-Muslim opinions. Although the Internet is significant in the development of contemporary society, no studies have focused on the importance of information and communication technologies in spreading Islamophobic opinions. However, the new technologies can also be used for monitoring and combating Islamophobia, and many Muslim organisations are today using the Internet for these purposes. The article is based on an indepth analysis of both anti-Muslim and pro-Muslim homepages that can be related to the debate over Islamophobia.     

Designing road safety interventions for young drivers – The power of peer influence

Peer passengers are associated with risky driving behaviour and increased collision rate in young drivers, but the mechanism by which young drivers are influenced by their peers is not well understood. Here we report two studies that explore the effect of peer influence on young drivers. The first explored the relationship between susceptibility to peer influence and young drivers’ engagement in risky driving behaviour. 163 young drivers completed self-report measures of risky driving behaviour and susceptibility to different forms of peer influence. Results showed that young drivers who were influenced by their peers to attain social prestige and through peers intervening in their decisions committed more driving violations. The second study sought to utilise the susceptibility of young drivers to peer influence by using peers to design and deliver a safety intervention, following the ‘U in the Driver Seat’ model from the US. When compared to a traditional fear appeal and a control, the peer intervention group reported safer attitudes and intentions to drive safely at follow-up. Together these studies provide insight into how peers influence young drivers’ risky behaviour, and support the notion of using peer education tools in young driver safety interventions.     

How many dimensions underlie judgments of learning and recall? Evidence from state-trace methodology

The authors used state-trace methodology to investigate whether a single dimension (e.g., strength) is sufficient to account for recall and judgments of learning (JOLs) or whether multiple dimensions (e.g., intrinsic and extrinsic factors) are needed. The authors separately manipulated the independent variables of intrinsic and extrinsic cues, determining their state traces for recall and JOLs. In contrast to the supposition that intrinsic cues have similar effects on both recall and JOLs whereas extrinsic cues affect JOLs less strongly than recall (i.e., 2 dimensions underlying recall and JOLs), the authors found repeated support for the sufficiency of a single dimension for both recall and JOLs (not only immediate JOLs but also delayed JOLs) across a variety of intrinsic and extrinsic cues.