David Navon

The forest revisited: More on global precedence

SummarySeveral issues pertaining to the notion of global precedence, its testing, and its ecological validity are discussed. Global precedence is presented as a claim that, other things being equal, global structure is available in the percept earlier than local features are. It does not state that local processing starts only after global processing is terminated. Since global precedence is a hypothesis about temporal development of percepts, a natural way to test it is to limit exposure duration. Global precedence predicts that local features will be more sensitive to stimulus duration than global ones.An experiment is reported in which subjects were presented with 150 ms exposures of large letters made up of small ones, and had to discriminate either just the large letters or just the small ones. In addition, they had to respond to the presence of a concurrent tone. Local letters were responded to more slowly than global ones, and were associated with more tone errors. The variation of the global level as well as the consistency between the identities of the levels affected the latency to the local letter, but not vice versa. A single small-letter control-condition was used to rule out an explanation in terms of relative size. The effects, albeit weaker than some previous results, are compatible with the hypothesis tested.The results of this experiment are interpreted in the context of an extensive discussion of findings in the paradigm and the generality of the phenomenon assumed to underly them. Possible mechanisms which may mediate global precedence are evaluated. Among them are relative size, lateral masking, diffuse attention, and spatial uncertainty. The magnitude, or even the presence, of global precedence depends on some factors, most prominent of which are visual angle and retinal position. Ecological considerations suggest that proximal sizes and eccentricities which favor global features may be very frequent. Some further subtleties of, as well as problems with, the logic of compound letters are discussed.

Queuing or Sharing? A Critical Evaluation of the Single-Bottleneck Notion ☆

The model of a single central bottleneck for human information processing is critically examined. Most evidence cited in support of the model has been observed within the overlapping tasks paradigm. It is shown here that most findings obtained within that paradigm and that were used to support the model are also consistent with a simple resource model. The most prominent findings are the millisecond-for-millisecond slope at the left of the RT2-SOA curve, the high RT1-RT2 correlation, the additivity of the effects on RT2 of SOA and of the difficulty of selecting R2, and the washout of the effect of S2 discriminability on RT2 in a dual-task condition. In addition, the asymmetry of the effects of the dual-task requirement on RT1 and RT2 can be accounted for by the resource model provided that it assumes uneven allocation of resources, which is quite reasonable in view of the task asymmetry inherent in the demand characteristics of the paradigm. The same is true for two other findings that appear to support the single-bottleneck model-that in the dual-task condition, the demand of the first task affects equally RT1 and RT2 and that its effect on RT1 is the same as the corresponding effect in the single-task condition. Furthermore, the single-bottleneck model is hard to reconcile with a negative slope at the left of the RT1-SOA curve or a positive slope at the left of the IRI-SOA curve, unless augmented by ancillary assumptions that are yet to be substantiated. Representative data were fit by each of the models using its optimal set of parameters. Both models achieved quite good degrees of fit. It is further argued that since the overlapping tasks paradigm is heavily biased in favor of a speedy reaction to the stimulus that appears first, it is nonoptimal for testing the central bottleneck model. Finally, the bottleneck model is examined in terms of other scientific criteria.

Role of outcome conflict in dual-task interference

The traditional explanation for dual-task interference is that tasks compete for scarce processing resources. Another possible explanation is that the outcome of the processing required for one task conflicts with the processing required for the other task (e.g., cross talk). To explore the contribution of outcome conflict to task interference, we manipulated the relatedness of the tasks. In Experiment 1, subjects searched concurrently for names of boys in one channel and names of cities in another channel. Responses were significantly delayed when a nontarget on one channel belonged to, or was even just related to, the category designated as the target for the other channel. No comparable effects were found when the tasks were performed in isolation. Thus, the difficulty of the individual tasks is not the only determinant of how much they will interfere when combined, and there must be substantial interactions between processes carrying out the two tasks. In Experiment 2 subjects searched one channel for specific target letters and another channel for specific target digits. The nontargets in a channel were either from the same alphanumeric category as the targets for that channel or from the opposite category (i.e., the category of the targets for the other channel). It was found that although between-category search was more efficient than within-category search in single tasks, it was less efficient in dual tasks. Thus, there appear to be significant task interactions due to the confusability emerging when the nontargets of one task belong to the same category as the targets of the concurrent task. In addition, the congruence of target presence or absence on the two channels was found to have a sizeable effect. We suggest four potential sources of outcome conflict that may contribute to dual-task interference, and we conjecture that a great deal of the residual interference might result from other sorts of outcome conflict.

The importance of being visible: On the role of attention in a mind viewed as an anarchic intelligence system i basic tenets

Abstract This paper describes an attempt to view attention from the perspective of a pluralistic concept of information processing in the mind. The mind is likened to an anarchic intelligence system. It is assumed to comprise of a set of processing entities called modules that may be active in parellel. Their activation is externally driven, and their operation is not controlled by any other module. Cooperating among modules is often required for achieving goals. Cooperation calls for communication. Attention is assumed to regulate only the communication among modules. It exerts attentional emphasis by making the output of a to-be-attended module available for a maximal number of other modules, while limiting the ability of de-emphasised modules to disseminate their output. This is achieved by a mechanism called decoupling that controls the connections between modules. The control of decoupling that is required for attentional emphasis is associated with an aversive phenomenal aspect that is usually calle...

Irrelevance of figural identity for resolving ambiguities in apparent motion.

In order to examine the degree to which form perception affects the formation of apparent-motion experience, subjects were presented with nine ambiguous apparent-motion situations, where the elements of each single flash were various figures. One of the interpretations of each situation preserved the figural identity of the figures across flashes. It was found that figural identity does not have any effect on determining the type of motion experienced, except when the figural analysis involved is relatively simple.

Different difficulty manipulations interact differently with task emphasis: Evidence for multiple resources.

To test the notion of multiple resources, a two-dimensional pursuit tracking task was paired with a letter-typing task, the difficulty of which was manipulated by varying cognitive (size of stimulus set) and motor (repetitiveness of finger chords) factors. In addition, task priority was manipulated. The latter factor had a large effect on the performance of the two tasks, which indicates that they compete for resources. Both types of typing difficulty manipulations affected typing performance, but only motor difficulty interacted with priorities. Since difficulty manipulations that tap resources common to both tasks are predicted to interact with priorities, the results are interpreted to indicate that in joint performance, typing and tracking compete mainly for motor-related concept, the letter-typing task is argued to require at least two kinds of resources.

How many trees does it take to make a forest

In order to study the relative perceptual availability of global and local features in very sparse patterns, subjects were asked to make ‘same’/‘different’ judgments on pairs of geometrical figures and the times needed to detect global and local differences were compared. With triangular patterns a global precedence was found which could be attributed to size differences. With rectangular patterns global precedence was larger, not accounted for by size differences, and indifferent both to the number of elements and to their spacing. Thus it was demonstrated that global precedence may hold for patterns with as few as four elements. Patterns with smooth edges could be compared much more quickly than patterns with serrated eges. It is proposed that configurational properties of some of the patterns interfered with the encoding of their global structures or with comparing them. It is argued that the results support a principle of global addressability which postulates that visual schemata are mainly addressed through their global constituents.

Do attention and decision follow perception Comment on Miller

In response to Millers discussion of global precedence, I argue that (a)although perceptual precedence is not the only explanation for asymmetric interference, in some cases it is the most reasonable one; (b) since global precedence does not entail that local and global information cannot interact in their effects on responses, the finding that they do is not incompatible with global precedence; (c) it is dubious that attention or decision are applied just to the resultant of perception rather than determining it or constituting part of it. However, I share some of Millers doubts about the unique contribution of asymmetric interference data in deciding the issue of global precedence.

Allocation of attention according to informativeness in visual recognition

In visual identification, is visual attention attracted to more informative elements, i.e. to elements which are more critical for identification? This question was investigated by having subjects detect some visual probes while performing a primary task that involved identification. The probes were located in the neighbourhood of highly or poorly informative parts of the identified stimuli. Three experiments that followed this rationale were conducted. In Experiment I, it was found that when subjects searched for a target letter in lines of identical background letters, they detected more dots near the feature that distinguished between the target and the background letters. In Experiment 11, it was found that native Hebrew-speaking subjects detected more lines above a letter that distinguished between two English words. Experiment III showed that the effect was reduced but did not vanish when spatial uncertainty was introduced. On the whole, the data are interpreted as suggesting that more attention may indeed be directed to informative regions, and that this effect cannot be solely attributed to retinal factors.

The importance of being visible: On the role of attention in a mind viewed as an anarchic intelligence system II. application to the field of attention

Abstract The view of attention presented in the first part of this paper is elaborated and is shown to accommodate most known phenomena in selective, divided, and sustained attention. It is also used to discuss the major issues in the domain of attention. The present approach to these issues is compared with other approaches. Finally, the stance of the present view with regard to the mind-body issue is discussed.