Capacity limits of information processing in the brain

doi:10.1016/j.tics.2005.04.010

Trends in Cognitive Sciences

Volume 9, Issue 6, June 2005, Pages 296-305

https://doi.org/10.1016/j.tics.2005.04.010 Get rights and content

Despite the impressive complexity and processing power of the human brain, it is severely capacity limited. Behavioral research has highlighted three major bottlenecks of information processing that can cripple our ability to consciously perceive, hold in mind, and act upon the visual world, illustrated by the attentional blink (AB), visual short-term memory (VSTM), and psychological refractory period (PRP) phenomena, respectively. A review of the neurobiological literature suggests that the capacity limit of VSTM storage is primarily localized to the posterior parietal and occipital cortex, whereas the AB and PRP are associated with partly overlapping fronto-parietal networks. The convergence of these two networks in the lateral frontal cortex points to this brain region as a putative neural locus of a common processing bottleneck for perception and action.

Section snippets

Capacity limit in explicit visual event detection: the attentional blink

Virtually all models of visual cognition distinguish between capacity–unlimited and capacity-limited stages of information processing (e.g. 3, 4). In these two-stage models, an early stage permits the rapid, initial evaluation of the visual world, whereas later attention-demanding, capacity-limited stages are necessary for the conscious report of the stimuli. The dual nature of visual cognition is well illustrated by the attentional blink (AB) paradigm: when subjects attempt to identify two

The neural basis of the AB bottleneck

Two-stage models of the AB have received considerable support from event-related potential (ERP) studies. T2 target words that are not explicitly perceived in an AB paradigm nonetheless elicit an N400, an electrophysiological marker of semantic processing [15], whereas successful detection of T2 elicits a P300 [9], an electrophysiological marker of working memory updating. Thus, T2 targets that fail to reach working memory are nevertheless processed up to the semantic level.

Functional magnetic

Capacity limits of visual short term memory (VSTM)

Our visual cognition is not only limited by the rate at which information can be attended or consolidated into VSTM, it is also limited by the amount of information that can be stored in VSTM. Although the capacity of VSTM is generally estimated to be about 4 items 28, 29, 30, it is set not only by the number of objects but also by the complexity of each object [31]. This capacity limit has significant behavioral consequences. For instance, VSTM storage capacity is thought to be at least partly

The neural basis of VSTM storage capacity limits

Visual working memory is mediated by a network of brain regions distributed across the cerebral cortex 41, 42, 43. This network can be loosely divided into regions that contribute to Baddeley's [34] central executive system, and regions involved in maintaining the information in working memory (i.e. VSTM). Executive processes, such as encoding, manipulation and retrieval of information from working memory, have been primarily associated with the frontal/prefrontal cortex 44, 45. By contrast,

The limits of response selection: the psychological refractory period

A third major bottleneck of information processing takes place when an appropriate action has to be selected in response to a stimulus. This is evidenced by the psychological refractory period (PRP) paradigm [55]: when subjects are required to perform two sensorimotor tasks in rapid succession, the response to the second task is increasingly delayed as the stimulus onset asynchrony (SOA) between the two tasks decrease (Figure 3a). This occurs even when sensory and motor modalities are distinct

Neural correlates of the psychological refractory period

Electrophysiological studies of the PRP have established the temporal boundary of the PRP bottleneck to a stage between stimulus consolidation in working memory and motor preparation 66, 67, and split-brain patient studies implicate a sub-cortical component to the PRP 68, 69. By contrast, imaging studies have primarily aimed at localizing the cortical substrates of the PRP. Although the neural basis of dual-task interference has received considerable attention over the past 10 years [70], only

Convergence of processing limitations?

This review has so far discussed capacity limits in encoding visual information in working memory (AB), in maintaining and monitoring that information (VSTM and MOT), and in selecting an appropriate response for it (PRP), as if these tapped into strictly independent stages of information processing. Indeed, perceptual and response limitations have traditionally been viewed as such [55]. However, this view has been challenged by findings that the AB and PRP partly share a common capacity-limited

The functional neuroanatomy of processing bottlenecks: a synthesis

Another approach to assessing the relationship between processing bottlenecks is to determine whether they engage similar neural substrates. Although demonstrating that two cognitive processes activate similar brain regions does not necessarily imply that these processes overlap at the cellular level, the failure to find such common foci of activation would rule out the possibility that these processes affect each other through a common neural substrate. Figure 4 shows the brain regions

Conclusion

This review of the literature supports the view that the neural substrates of VSTM storage capacity are primarily localized to posterior cortical regions, and predicts that distinct regions of visual cortex may contribute to separate forms of VSTM storage capacity. By contrast, the AB and PRP bottlenecks are most likely to result from the interaction between foci of a distributed fronto-parietal – and probably visual – cortical network, with individual nodes of the network (e.g. lateral frontal

Acknowledgements

This work was supported by grants from NSF and NIMH to R.M. and from CICN and NSERC (Canada) to J.I.

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Trends in Cognitive Sciences

Capacity limits of information processing in the brain

Section snippets

Capacity limit in explicit visual event detection: the attentional blink

The neural basis of the AB bottleneck

Capacity limits of visual short term memory (VSTM)

The neural basis of VSTM storage capacity limits

The limits of response selection: the psychological refractory period

Neural correlates of the psychological refractory period

Convergence of processing limitations?

The functional neuroanatomy of processing bottlenecks: a synthesis

Conclusion

Acknowledgements

Trends Cogn. Sci.

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Neuroimage

Neuron

Curr. Opin. Neurobiol.

Trends Cogn. Sci.

Neuron

Cogn. Psychol.

Brain Res. Cogn. Brain Res.

Neuroimage

Cogn. Psychol.

Neuron

The Computer and The Brain

A two-stage model for multiple target detection in rapid serial visual presentation

J. Exp. Psychol. Hum. Percept. Perform.

Temporary suppression of visual processing in an RSVP task: an attentional blink?

J. Exp. Psychol. Hum. Percept. Perform.

Direct measurement of attentional dwell time in human vision

Nature

Task switching mediates the attentional blink even without backward masking

Percept. Psychophys.

Modulation of the attentional blink by on-line response selection: evidence from speeded and unspeeded Task-sub-1 decisions

Mem. Cogn.

Electrophysiological evidence for a postperceptual locus of suppression during the attentional blink

J. Exp. Psychol. Hum. Percept. Perform.

The attentional blink and task switching within and across modalities

Restricted attentional capacity within but not between sensory modalities

Nature

Modality-specific auditory and visual temporal processing deficits

Q J Exp Psychol A

Concurrent response-selection demands modulate the attentional blink

J. Exp. Psychol. Hum. Percept. Perform.

Perceptual and central interference in dual-task performance

Word meanings can be accessed but not reported during the attentional blink

Nature

Cerebral mechanisms of word masking and unconscious repetition priming

Nat. Neurosci.

Neural correlates of change detection and change blindness

Nat. Neurosci.

Abnormal temporal dynamics of visual attention in spatial neglect patients

Nature

Qualitative differences in the representation of spatial relations for different object classes

J. Exp. Psychol. Hum. Percept. Perform.

Modulation of long-range neural synchrony reflects temporal limitations of visual attention in humans

Proc. Natl. Acad. Sci. U. S. A.

A neuronal network model linking subjective reports and objective physiological data during conscious perception

Proc. Natl. Acad. Sci. U. S. A.

The magical number 4 in short-term memory: a reconsideration of mental storage capacity

Behav. Brain Sci.

The capacity of visual working memory for features and conjunctions

Nature

Familiarity and visual change detection

Percept. Psychophys.

The capacity of visual short term memory is set both by visual information load and by number of objects

Psychol. Sci.

Change detection

Annu. Rev. Psychol.