Temporal binding due to causality

ScienceDaily has an item (here) reporting a paper by Marc J. Buehner, Understanding the Past, Predicting the Future: Causation, not Intentional Action, is the Root of Temporal Binding, in Psychological Science.

 

When events happen close together in time and space they can be bound together as part of the same meaningful episode. And further more they are perceived to be closer together in time. This has been called temporal binding.

Research has shown that our perceptual system seems to pull causally-related events together — compared to two events that are thought to happen of their own accord, we perceive the first event as occurring later if we think it is the cause and we perceive the second event as occurring earlier if we think it is the outcome.

 

This has been thought to be due to motor intention.

Some researchers have hypothesized that our perceptual system binds events together if we perceive them to be the result of intentional action, and that temporal binding results from our ability to link our actions to their consequences.

 

Buehner questioned this hypothesis.

“We already know that people are more likely to infer a causal relation if two things are close in time. It follows, via Bayesian calculus, that the reverse should also be true: If people know two things are causally related, they should expect them to be close in time,” Buehner says. “Time perception is inherently uncertain, so it makes sense for systematic biases in the form of temporal binding to kick in. If this is true, then it would suggest that temporal binding is a general phenomenon of which intentional action is just a special case.”

 

He compared time predictions of baseline events, events caused by the subject, and events caused by a machine. The time prediction of events caused by the subject and by a machine were the same and differed from the baseline events which were not causally related. Intentionality is not the cause of the binding, perceived causality was. “Causation instills a subjective time warp in people’s minds.

The LIDA model

Madl, Baars and Franklin have proposed a model of cognition they call LIDA (Learning Intelligent Distribution Agent). It is a series of cycles, each cycle preforming an ‘atom’ of cognition. (see citation below) A series of these ‘atoms’ would make up the performance of a cognitive task (problem solving, deliberation, volitional decision making for example). LIDA is an elaboration of the global workspace theory but takes under its wing other theories – they site embodied cognition, perceptual symbol systems, working memory, memory by affordances, long-term working memory, transient episodic memory, H-CogAff cognitive architecture, and Action Selection paradigm as contributing.

 

Here is their description of the Global Workspace idea:

The global workspace theory can be thought of as ‘‘… a theater of mental functioning. Consciousness in this metaphor resembles a bright spot on the stage of immediate memory, directed there by a spotlight of attention under executive guidance. Only the bright spot is conscious, while the rest of the theater is dark and unconscious’’. In case of sensory consciousness, the stage corresponds to the sensory projection areas of the cortex, its activation coming either from senses or from internal sources. After a conscious sensory content is established, it is distributed to a decentralized ‘‘audience’’ of expert networks sitting in the darkened theater. Thus, the primary functional purpose of consciousness is to integrate, provide access, and coordinate the functioning of very large numbers of specialized networks that otherwise operate autonomously. In the neuroscientific study of consciousness, this idea of consciousness having an integrative function has proven very useful, and is supported by much recent evidence.

 

This global workspace is where consciousness occurs, just once in each cognitive cycle. The cycle goes through perceive – understand – act and back to perceive. They strongly state that in LIDA these three types of process run continuously and are not confined to a particular block of time. But consciousness does occur only once and for a limited time in each cycle.

The most impressive aspect of this paper for me was their review of many published measurements of timing in the brain. The LIDA cycle is based on the theta rhythm and the gamma rhythm synchronizations phase locked to it. In the end they settle on a timing for a cycle based on their review:

t0 stimulus start

perception (80-100ms)

understanding (perception & understanding together = unconscious processing)

unconscious processing (260-280ms)

conscious broadcasting

action selection (60-110ms) (cannot start before conscious broadcasting)

total cognitive cycle (260-390ms)

 

I may return to this paper in future postings as there are some very interesting corners in it. This model has consciousness as distinct frames, however they do allow for elements from previous frames to linger. It also has a number of memory stores in its scheme: sensory memory, perceptual associative memory, transient episodic memory, declarative memory, procedural memory, sensory-motor memory. These are for future postings.

 

The LIDA model has been stimulated by computer programs and tested in very simple scenarios in preparation for more elaborate stimulations.

 

Here is the abstract :

We propose that human cognition consists of cascading cycles of recurring brain events. Each cognitive cycle senses the current situation, interprets it with reference to ongoing goals, and then selects an internal or external action in response. While most aspects of the cognitive cycle are unconscious, each cycle also yields a momentary ‘‘ignition’’ of conscious broadcasting. Neuroscientists have independently proposed ideas similar to the cognitive cycle, the fundamental hypothesis of the LIDA model of cognition. High-level cognition, such as deliberation, planning, etc., is typically enabled by multiple cognitive cycles. In this paper we describe a timing model LIDA’s cognitive cycle. Based on empirical and simulation data we propose that an initial phase of perception (stimulus recognition) occurs 80–100 ms from stimulus onset under optimal conditions. It is followed by a conscious episode (broadcast) 200–280 ms after stimulus onset, and an action selection phase 60–110 ms from the start of the conscious phase. One cognitive cycle would therefore take 260–390 ms. The LIDA timing model is consistent with brain evidence indicating a fundamental role for a theta-gamma wave, spreading forward from sensory cortices to rostral corticothalamic regions. This posteriofrontal theta-gamma wave may be experienced as a conscious perceptual event starting at 200–280 ms post stimulus. The action selection component of the cycle is proposed to involve frontal, striatal and cerebellar regions. Thus the cycle is inherently recurrent, as the anatomy of the thalamocortical system suggests. The LIDA model fits a large body of cognitive and neuroscientific evidence. Finally, we describe two LIDA-based software agents: the LIDA Reaction Time agent that simulates human performance in a simple reaction time task, and the LIDA Allport agent which models phenomenal simultaneity within timeframes comparable to human subjects. While there are many models of reaction time performance, these results fall naturally out of a biologically and computationally plausible cognitive architecture.

 

I was a bit surprised that there was no mention of a small prediction being built into the workspace contents. This is really needed for error monitoring in cognition and action. Surely this will be part of the model at some point in its development.

 

 

ResearchBlogging.org

Madl, T., Baars, B., & Franklin, S. (2011). The Timing of the Cognitive Cycle PLoS ONE, 6 (4) DOI: 10.1371/journal.pone.0014803

Rhythm

When I imagine a sort-of-core to my being, knowing this to be an will-o-the-wisp, what I find is rhythms: breathing, heartbeat, walking, speech cadence and so on, all those cyclic or tick-tocking things my body does. I have never taken that feeling too seriously but looking at consciousness seems to re-enforce the motif of rhythm.

 

Mehta’s group has just published a paper (see citation) on the effect of movement on hippocampal gamma waves. The results in this study are very clear cut and convincing.

Here is the abstract:

Cortical and hippocampal gamma oscillations have been implicated in many behavioral tasks. The hippocampus is required for spatial navigation where animals run at varying speeds. Hence we tested the hypothesis that the gamma rhythm could encode the running speed of mice. We found that the amplitude of slow (20–45 Hz) and fast (45–120 Hz) gamma rhythms in the hippocampal local field potential (LFP) increased with running speed. The speed-dependence of gamma amplitude was restricted to a narrow range of theta phases where gamma amplitude was maximal, called the preferred theta phase of gamma. The preferred phase of slow gamma precessed to lower values with increasing running speed. While maximal fast and slow gamma occurred at coincident phases of theta at low speeds, they became progressively more theta-phase separated with increasing speed. These results demonstrate a novel influence of speed on the amplitude and timing of the hippocampal gamma rhythm which could contribute to learning of temporal sequences and navigation.

 

Conscious awareness appears to predict the near future but I have not encountered a clear mechanism or description of what parts of the content of consciousness is projected forward. This paper shows that the navigation system in the hippocampus changes with the speed of movement. In effect it seems possible that the ‘here’ spot in a mental place map is biased by the speed of movement. So the faster we are traveling the more we feel projected up the road. This would be a start to understanding how the prediction involved in consciousness is produced.

 

Another thing that I found interesting although not entirely new was the idea of control via the phases of a slower wave. The theta wave is in the region of 6 Hz (or has about 6 peaks per second) and the gamma waves are much faster say 60 Hz for example (or 60 peaks per second). In the case of gamma in this region of the brain, they occur with the highest amplitude as the theta wave nears its trough. This type of mechanism can give very complex cyclical activity with different activities happening in sequence as the longer wave runs from a peak to a trough and then back to a peak. It even seems, on the basis of this study, that the sequence can be affected by some input such as the speed of movement. Consciousness is characterized by cycles of increasing and then decreasing gamma wave synchrony between cortical areas, possibly due to phrase locking to a theta-type rhythm. We are so far from understanding but a step closer.

 

 

ResearchBlogging.org

Chen, Z., Resnik, E., McFarland, J., Sakmann, B., & Mehta, M. (2011). Speed Controls the Amplitude and Timing of the Hippocampal Gamma Rhythm PLoS ONE, 6 (6) DOI: 10.1371/journal.pone.0021408

Motor bias

Eagleman and Sejnowski report a series of experiments that go a long way to pinning down the nature of our conscious perception of movement. A number of illusions were used in experiments showing that they shared a common process: flash-lag (moving object aligned with flash is offset), flash-drag (flash is offset as result of nearby motion), feature flash-drag (a change in a moving object is mis-located) and Frohlich illusion (the starting position of a suddenly appearing moving object is offset). The question that the researchers were answering is whether it is the position or the time that is altered in these illusion.

By varying the classic setups, the researchers found they could have the consciously perceived location of an object to be at a position where the object could not have physically been. Thus the illusion could not be based on an actual location with a fiddled time. It was the position that was being fiddled.

Several other characteristics of motion bias were also shown in the experiments.

  • In all the setups, there was a trigger, a particular event for the subject to use as the reference for ‘now’. The motion that was used to bias the position occurs after the trigger during about the next 80 ms and not before the trigger.

  • There does not appear to be two types of perception, one for stationary and one for moving objects. “the configuration of motion in the visual field influences the localization of both moving and stationary stimuli”. There can therefore be a trade-off between flash lag and flash drag.

  • Where features like colour change during the motion of an object. The binding of the feature is not changed but only the position of the object when the change is bound to it.

One aspect of the discussion is a problem for me. The authors appear to consider only one reason for this motion biasing. “The visual system attempts to correct for the processing delays in signals from eye to perception and accounts for these delays by shifting its localizations closer to where they would be if there were no neural delay.” They also assume, “localization computations might only be triggered on a need-to-know basis. If true, this suggests that it may be computationally expensive”.

I have for some time thought that prediction of the very near future was one of the functions (perhaps the main function) of consciousness. Far from the idea that prediction is only an occasional operation in ‘need to know’ situations, I think it may be continuously done with all motion all the time. As well as removing the experience of a lag in ‘now’, there for two other reasons for prediction. Comparison of predictive conscious experience with fresh sensory information is a possible method of monitoring the accuracy of perception and checking the validity of our understanding of the world. It is also a possible method for avoiding motor plans that conflict with each other and instead facilitate smoothly integrated motor programs.

ResearchBlogging.org
Eagleman, D., & Sejnowski, T. (2007). Motion signals bias localization judgments: A unified explanation for the flash-lag, flash-drag, flash-jump, and Frohlich illusions Journal of Vision, 7 (4), 3-3 DOI: 10.1167/7.4.3

A step towards correlates of consciousness

There are only a few ways to watch the brain in action and one is to follow its electromagnetic waves. Doesburg and his group have looked at the waves that accompany conscious awareness. They use binocular rivalry to mark when the content of consciousness changes (If different images are sent to the two eyes, we are not conscious of a mixed image but of one or the other alternatively and the changes can be reported.) and a key press to indicate a change in the conscious perception. The work confirms previous EEG measurements of conscious processes including:

  • Low gamma-band (30-50Hz) synchronization between neural groups codes the various features of objects and binds them into the perceptual experience. Neurons in synchrony communicate.

  • Remote gamma-band EEG phase synchronization index the onset of coherent visual perception and is associated with conscious rather than unconscious processes.

  • Gamma-band synchronization between the hemispheres is required for integration of sense input from the two hemispheres into consciousness.

  • Synchronized gamma waves between the thalamus and cortex as well as within the cortex is associated with consciousness. Disruption of thalamo-cortical communication is the nature of anesthesia.

  • Gamma-band synchronization increases and decreases in an oscillation. This gives the attentional blink when the synchronization is low and accounts for the ‘frames’ of working memory.

 

The study also adds valuable insights:

  • Large-scale gamma-band synchronization constitutes an oscillatory substrate for the stream of consciousness. The oscillation is due to the gamma waves being found in only one portion of the theta-band waves (4-7Hz). “onset of a new percept … time-locked bursts of gamma-band activation that recur at a theta rate.”

  • The prefrontal cortex and parietal lobe are essential parts of the ‘consciousness network’. Probably the prefrontal cortex is relevant for integration and self-awareness and the parietal cortex supplies the multimodal representation of space. The primary visual cortex was not generating time-locked gamma rhythms. “This supports the view that the large-scale oscillatory network detailed here is essentially related to perceptual experience itself, and not to those unconscious functions to give rise to changes within it.” In other words, the gamma synchronization that is local to the visual cortex is not to be confused with the remote synchronization that occurs from the parietal lobe.

  • The content of consciousness need not be completely new in each ‘frame’. “continuous viewing of a single unchanging stimulus will yield a procession of theta cycles in which the content remains the same.” When there is a change of content, the inferior temporal cortex is involved in the synchrony and when motor response is required so is the motor cortex.

  • There are differences in the phase of the theta wave during which area pairs become synchronous. In other words along a part of the theta wave various areas join and leave the gamma synochrony. This is probably not a single event but an ordered process.

 

Here is their abstract:

Consciousness has been proposed to emerge from functionally integrated large-scale ensembles of gamma-synchronous neural populations that form and dissolve at a frequency in the theta band. We propose that discrete moments of perceptual experience are implemented by transient gamma-band synchronization of relevant cortical regions, and that disintegration and reintegration of these assemblies is time-locked to ongoing theta oscillations. In support of this hypothesis we provide evidence that (1) perceptual switching during binocular rivalry is time-locked to gamma-band synchronizations which recur at a theta rate, indicating that the onset of new conscious percepts coincides with the emergence of a new gamma-synchronous assembly that is locked to an ongoing theta rhythm; (2) localization of the generators of these gamma rhythms reveals recurrent prefrontal and parietal sources; (3) theta modulation of gamma-band synchronization is observed between and within the activated brain regions. These results suggest that ongoing theta-modulated-gamma mechanisms periodically reintegrate a large-scale prefrontal-parietal network critical for perceptual experience. Moreover, activation and network inclusion of inferior temporal cortex and motor cortex uniquely occurs on the cycle immediately preceding responses signaling perceptual switching. This suggests that the essential prefrontal-parietal oscillatory network is expanded to include additional cortical regions relevant to tasks and perceptions furnishing consciousness at that moment, in this case image processing and response initiation, and that these activations occur within a time frame consistent with the notion that conscious processes directly affect behaviour.

 

ResearchBlogging.org
Doesburg, S., Green, J., McDonald, J., & Ward, L. (2009). Rhythms of Consciousness: Binocular Rivalry Reveals Large-Scale Oscillatory Network Dynamics Mediating Visual Perception PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006142

The clock speed of perceptual experience

Horowitz and group investigated the timing of attention shifts with a number of clever experiments aimed at separating the contributions to the total time of elements of attention shifts.

Abstract: Do voluntary and task-driven shifts of attention have the same time course? In order to measure the time needed to voluntarily shift attention, we devised several novel visual search tasks that elicited multiple sequential attentional shifts. Participants could only respond correctly if they attended to the right place at the right time. In control conditions, search tasks were similar but participants were not required to shift attention in any order. Across five experiments, voluntary shifts of attention required 200– 300 ms. Control conditions yielded estimates of 35 – 100 ms for task-driven shifts. We suggest that the slower speed of voluntary shifts reflects the “clock speed of free will”. Wishing to attend to something takes more time than shifting attention in response to sensory input.

I find this an excellent investigation except for the characterization ‘clock speed of free will’. They do describe this time in other words in the General Discussion.

It is possible to overrule this autonomous agent and select the next object of attention. This volitional deployment is much slower than the autonomous, priority-driven mode. We propose that the slower rate reflects the “clock speed of free will”. It might also reflect the clock speed of perceptual experience. Even if we can search through a display at 20-40 items/second, we do not experience 20-40 discrete selection events. We experience the search and its outcome but the rapid autonomous deployments of attention that are revealed by experiments are not available to consciousness. (underline added)

The ideas of free will and perceptual experience are distinct and different, very much so. The group’s careful experiments clearly showed a clock speed for perceptual experience and not for free will (whatever that is – as they do not define their use of the term). Scientists should be very careful about using terms with very wide range of meanings, in this case meanings ranging from the supernatural to the trivially mundane. It would also be wise to avoid terms that carry emotional, philosophical and political baggage unless this baggage is going to be ‘unpacked’.

 

ResearchBlogging.org
Horowitz, T., Wolfe, J., Alvarez, G., Cohen, M., & Kuzmova, Y. (2009). The speed of free will The Quarterly Journal of Experimental Psychology, 62 (11), 2262-2288 DOI: 10.1080/17470210902732155

Not convincing

ScienceDaily has an item on research by G.Kuhn and others on whether autism would effect the perception of illusions. (here) I find this research unconvincing as reported by ScienceDaily. As the original paper is not free on line, I have not been able to read it.

Magicians rely on misdirection — drawing attention to one place while they’re carrying out their tricky business somewhere else. It seems like people with autism should be less susceptible to such social manipulation. But a new study in the U.K. finds that people with autism spectrum disorder are actually more likely to be taken in by the vanishing ball trick, where a magician pretends to throw a ball in the air but actually hides it in his hand.

There appears to be an assumption that all magic tricks rely on social manipulation. Manipulation yes, but not always social manipulation. This illusion has nothing to do with social clues and it can be done with an obviously mechanical machine. The illusion is due to the prediction of a motion in the consciousness. Everyone who has a conscious awareness of the event will see the ball leave the hand as it did on several previous movements of the hand. This type of illusion is well known and well studied.

I am sure that it is a good idea to use illusions to understand conditions like autism, but it would be a good course to first understand why the illusion works for normal people.

The researchers keep ‘digging’ when they try to explain the results (at least in the ScienceDaily summary). Conscious experience is not a simple, straight forward phenomenon that can just be taken at face value especially when looking at illusions. All magician’s tricks are not based on just social manipulation.

follow the beat

ScienceDaily has an item on a paper by R. Canolty and others from the Carmena lab, Oscillatory phase coupling coordinates anatomically dispersed functional cell assemblies. (here)

They looked at data accumulated in other research over a number of years and analyzed the recordings to try to find linkages between firing frequencies. Here is the abstract:

Hebb proposed that neuronal cell assemblies are critical for effective perception, cognition, and action. However, evidence for brain mechanisms that coordinate multiple coactive assemblies remains lacking. Neuronal oscillations have been suggested as one possible mechanism for cell assembly coordination. Prior studies have shown that spike timing depends upon local field potential (LFP) phase proximal to the cell body, but few studies have examined the dependence of spiking on distal LFP phases in other brain areas far from the neuron or the influence of LFP–LFP phase coupling between distal areas on spiking. We investigated these interactions by recording LFPs and single-unit activity using multiple microelectrode arrays in several brain areas and then used a unique probabilistic multivariate phase distribution to model the dependence of spike timing on the full pattern of proximal LFP phases, distal LFP phases, and LFP–LFP phase coupling between electrodes. Here we show that spiking activity in single neurons and neuronal ensembles depends on dynamic patterns of oscillatory phase coupling between multiple brain areas, in addition to the effects of proximal LFP phase. Neurons that prefer similar patterns of phase coupling exhibit similar changes in spike rates, whereas neurons with different preferences show divergent responses, providing a basic mechanism to bind different neurons together into coordinated cell assemblies. Surprisingly, phase-coupling–based rate correlations are independent of interneuron distance. Phase-coupling preferences correlate with behavior and neural function and remain stable over multiple days. These findings suggest that neuronal oscillations enable selective and dynamic control of distributed functional cell assemblies.

And here is an analogy, making the general picture easier to imagine:

“It is like the radio communication between emergency first responders at an earthquake,” Canolty said. “You have many people spread out over a large area, and the police need to be able to talk to each other on the radio to coordinate their action without interfering with the firefighters, and the firefighters need to be able to communicate without disrupting the EMTs. So each group tunes into and uses a different radio frequency, providing each group with an independent channel of communication despite the fact that they are spatially spread out and overlapping.”

For example, the high-beta band — 25 to 40 hertz (cycles per second) — was especially important for brain areas involved in motor control and planning. Other ‘channels’ would be used by other functions.

Sense of time


ScienceDaily has an item on research by A. Graybiel, ‘Neural representation of time in corticobasal ganglia circuits’. ( here )

“Keeping track of time is one of the brain’s most important tasks. As the brain processes the flood of sights and sounds it encounters, it must also remember when each event occurred. But how does that happen? … For decades, neuroscientists have theorized that the brain “time stamps” events as they happen, allowing us to keep track of where we are in time and when past events occurred. However, they couldn’t find any evidence that such time stamps really existed — until now … The research team trained two macaque monkeys to perform a simple eye-movement task. After receiving the “go” signal, the monkeys were free to perform the task at their own speed. The researchers found neurons that consistently fired at specific times — 100 milliseconds, 110 milliseconds, 150 milliseconds and so on — after the “go” signal … The neurons are located in the prefrontal cortex and the striatum, both of which play important roles in learning, movement and thought control. … We have sensory receptors for light, sound, touch, hot and cold, and smell, but we don’t have sensory receptors for time. This is a sense constructed by the brain.”

It strikes me that this clock system would be one more or less dedicated to motor processes because: it measures very short durations; it is found in the prefrontal cortex/striatum system; and it is more accurate than flexible. The conscious feeling of the passage of time may be from another system derived from this one or even a completely separate system.

The New Scientist had an article on time perception (here) by D. Fox that reviews a number of experiments.

  • R. VanRullen showed that vision is framed rather than continuous and the frame rate is about 13 per second. He found that the visual area of the right inferior parietal lobe generated a 13 Hertz wave. The question then was – is the framing global or independent for each preceived object? Visual illusions showed that framing is not global.

“This implies that there is not a single “film roll” in the brain, but many separate streams, each recording a separate piece of information. What’s more, this way of dealing with incoming information may not apply solely to motion perception. Other brain processes, such as object or sound recognition, might also be processed as discrete packets.”

  • Using very weak stimuli he showed that there are windows of perception.

“… found that the likelihood of them noticing the light depended on the phase of another wave in the front of the brain, which rises and falls about 7 times per second. It turned out that subjects were more likely to detect the flash when the wave was near its trough, and miss it when the wave was near its peak. There’s a succession of ‘on’ periods and ‘off’ periods of perception. Attention is collecting information through snapshots … So it seems that each separate neural process that governs our perception might be recorded in its own stream of discrete frames. But how might all these streams fit together to give us a consistent picture of the world?”

  • E. Poppel looked at this problem, proposed blocks of frames and found some experimental evidence for the blocks.

“… separate snapshots from the senses may feed into blocks of information in a higher processing stream. He calls these the “building blocks of consciousness” and reckons they underlie our perception of time. … It’s an appealing idea, since patching together a chronological order of events hitting our senses is no mean feat. Sounds tend to be processed faster than images, so without some sort of grouping system we might, say, hear a vase smashing before we see it happen. Pöppel’s building blocks of consciousness would neatly solve this problem: if two events fall into the same building block, they are perceived as simultaneous; if they fall into consecutive buildings blocks, they seem successive. Perception cannot be continuous because the limits of neural processing. …. A space of 30 to 50 milliseconds is necessary to bring together in one time-window the distributed activity in the neural system.”

There is also interesting discussion of whether our sense of time becoming slower or faster is a function of brain speed or of memory density. And finally exploration of the idea that some symptoms of schizophrenia may be due to faulty timekeeping.

Clock speeds


Look at the frequency of some events: the gamma waves that synchronize the thalamus and large parts of the cortex happen between 25 and 100 times per second but typically near 40; the saccadic eye vibrations happen between 30 and 70 times per second; the flicker rate of movie projectors that makes the picture stable is between 48 and 72 times per second. This makes one guess that there is a good probability that the discontinuous nature of the ‘frames’ from the eye, from a movie screen and from consciousness all have the same timing centered on about 50 Hz. A group has now shown that the focus of attention shifts about 18 to 34 times a second and averages about 25 Hz. It looks like two frames per focus.

This attention timing is reported by ScienceDaily (here) in an item on a paper by T. Buschman and E. Miller.

You’re meeting a friend in a crowded cafeteria. Do your eyes scan the room like a roving spotlight, moving from face to face, or do you take in the whole scene, hoping that your friend’s face will pop out at you? And what, for that matter, determines how fast you can scan the room?…. you are more likely to scan the room, jumping from face to face as you search for your friend. In addition, the timing of these jumps appears to be determined by waves of activity in the brain that act as a clock. …the study showed that brain waves act as a kind of built-in clock that provides a framework for shifting attention from one location to the next. … Buschman found that the spotlight of the mind’s eye shifted focus at 25 times a second and that this process of switching was regulated by brain waves. …the speed at which the animals searched was related to the speed of their brain waves. When the clock ticked faster, the animals “thought” faster.

The paper’s summary is below:

Attention regulates the flood of sensory information into a manageable stream, and so understanding how attention is controlled is central to understanding cognition. Competing theories suggest visual search involves serial and/or parallel allocation of attention, but there is little direct, neural evidence for either mechanism. Two monkeys were trained to covertly search an array for a target stimulus under visual search (endogenous) and pop-out (exogenous) conditions. Here, we present neural evidence in the frontal eye fields (FEF) for serial, covert shifts of attention during search but not pop-out. Furthermore, attention shifts reflected in FEF spiking activity were correlated with 18–34 Hz oscillations in the local field potential, suggesting a “clocking” signal. This provides direct neural evidence that primates can spontaneously adopt a serial search strategy and that these serial covert shifts of attention are directed by the FEF. It also suggests that neuron population oscillations may regulate the timing of cognitive processing.