Brain changes in dyslexia - different in Hong Kong and Chicago

Siok et al show that the brain changes associated with dyslexia in an alphabetic versus an ideographic language can be different. In alphabetic language, a reader sees a letter and associates it with a sound. Chinese characters correspond to syllables and require much more memorization. Both Chinese and English dyslexics find it harder to make their way through even fairly simple written material. This study suggests that their brain mechanics as they try to read may be as different as Chinese is from English. Here is their abstract:

Developmental dyslexia is a neurobiologically based disorder that affects approximately 5–17% of school children and is characterized by a severe impairment in reading skill acquisition. For readers of alphabetic (e.g., English) languages, recent neuroimaging studies have demonstrated that dyslexia is associated with weak reading-related activity in left temporoparietal and occipitotemporal regions, and this activity difference may reflect reductions in gray matter volume in these areas. Here, we find different structural and functional abnormalities in dyslexic readers of Chinese, a nonalphabetic language. Compared with normally developing controls, children with impaired reading in logographic Chinese exhibited reduced gray matter volume in a left middle frontal gyrus region previously shown to be important for Chinese reading and writing. Using functional MRI to study language-related activation of cortical regions in dyslexics, we found reduced activation in this same left middle frontal gyrus region in Chinese dyslexics versus controls, and there was a significant correlation between gray matter volume and activation in the language task in this same area. By contrast, Chinese dyslexics did not show functional or structural (i.e., volumetric gray matter) differences from normal subjects in the more posterior brain systems that have been shown to be abnormal in alphabetic-language dyslexics. The results suggest that the structural and functional basis for dyslexia varies between alphabetic and nonalphabetic languages.

Simple curves can influence whether we see happy or sad faces.

Here is an interesting bit of work from Xu et al. showing that adaptation to simple stimuli (like the shape of a mouth) that are processed early in the visual hierarchy can influence our perception of higher level perceptions (i.e., of faces) that are analyzed at higher levels of the visual hierarchy. Thus adaptation to a concave (sad) cartoon mouth shape makes subsequent perception more likely to report a happy face, and vice versa. Their abstract:

Adaptation is ubiquitous in sensory processing. Although sensory processing is hierarchical, with neurons at higher levels exhibiting greater degrees of tuning complexity and invariance than those at lower levels, few experimental or theoretical studies address how adaptation at one hierarchical level affects processing at others. Nevertheless, this issue is critical for understanding cortical coding and computation. Therefore, we examined whether perception of high-level facial expressions can be affected by adaptation to low-level curves (i.e., the shape of a mouth). After adapting to a concave curve, subjects more frequently perceived faces as happy, and after adapting to a convex curve, subjects more frequently perceived faces as sad. We observed this multilevel aftereffect with both cartoon and real test faces when the adapting curve and the mouths of the test faces had the same location. However, when we placed the adapting curve 0.2° below the test faces, the effect disappeared. Surprisingly, this positional specificity held even when real faces, instead of curves, were the adapting stimuli, suggesting that it is a general property for facial-expression aftereffects. We also studied the converse question of whether face adaptation affects curvature judgments, and found such effects after adapting to a cartoon face, but not a real face. Our results suggest that there is a local component in facial-expression representation, in addition to holistic representations emphasized in previous studies. By showing that adaptation can propagate up the cortical hierarchy, our findings also challenge existing functional accounts of adaptation.

Here are some examples of face stimuli used in the studies, in which subjects were experiments as well as naive subjects:


Figure - Examples of the face stimuli used in this study. a, Cartoon faces used in experiment 1, generated with our anti-aliasing program. The mouth curvature varied from concave to convex to produce sad to happy expressions. b, Ekman faces used in experiment 2. The first (sad) and last (happy) images were taken from the Ekman PoFA database, and the intermediate ones were generated with MorphMan 4.0. c, MMI faces used in experiments 3 and 4. The first (sad), middle (neutral), and last (happy) images were taken from the MMI face database, and the other images were generated with MorphMan 4.0.

Infants to adults, color perception switches from right to left hemisphere

An interesting article by Franklin et al. shows that our perception of color categories (CP) starts in the right hemisphere, but then switches to the left hemisphere as it develops the lexical color codes of language. They suggest that language-driven CP in adults may not build on prelinguistic CP, but that language instead imposes its categories on a left hemisphere that is not categorically prepartitioned.

The 'size' of an odor can influence our reaching to grasp an object.

An nice example from Tubaldi et al. of multisensory integration. They find that olfactory information contains highly detailed information able to elicit the planning for a reach-to-grasp movement suited to interact with the evoked object. From their paper:

The size of the object evoked by the odour has the potential to modulate hand shaping. Importantly, the fact that ‘size’ olfactory information modulates the hand at the level of individual digits (and not only the thumb-index distance as previously reported) leads to two important considerations in terms of sensorimotor transformation. First, from a perceptual perspective, the representation evoked by the odour seems to contain highly detailed information about the object (i.e., volumetric features rather than a linear dimension such as the thumb-index distance). If olfaction had provided a blurred and holistic object's representation (i.e., a low spatial-resolution of the object's image), then the odour would have not affected the hand in its entirety. Second, from a motor perspective, the olfactory representation seems to be mapped into the action vocabulary with a certain degree of reliability. The elicited motor plan embodies specific and selective commands for handling the ‘smelled’ object, and it is fully manageable by the motor system. Therefore, it is not an incomplete primal sketch which only provides a preliminary descriptive in the terms of motor execution.

Some of the details:

When the odour was ‘large’ and the visual target was small, only one finger joint (i.e., the mcp joint of the ring finger) was affected by the olfactory stimulus. In contrast, the influence of the ‘small’ odour on the kinematics of a reach-to-grasp movement towards a large target was much more evident and a greater number of joints were mobilized. This seems to suggest that planning for a reach-to-grasp movement on the basis of a ‘small’ odour when the target is large poses more constraints than when the odour is ‘large’ and the movement is directed towards a small target. Our proposal is that the motor plan elicited by the odour has to be modified according to the visual target. However such reorganization could be more easily managed without compromising object grasp when the odour is ‘large’ and the visual target is small than vice versa.

When a preceding odour elicits a motor plan which is congruent with the motor plan subsequently established for the visual target, the kinematic patterning is magnified. Therefore, the grasp plan triggered by the olfactory stimulus primed the grasp plan established for the visual target. This effect was evident at the very beginning of the movement, fading away during the second phase of the movement. For both the incongruent conditions the conflict between the ‘olfactory’ and the ‘visual’ grasp plans lasted for the entire movement duration. Importantly, and again in contrast with what reported for the incongruent conditions, an odour of a similar ‘size’ than the visual target, does not alter hand synergies with respect to when no-odour is presented. This indicates that when the ‘size’ of the odour and the size of the visual target match, the integration of the two modalities reinforces the grasp plan, the established synergic pattern is more ‘protected’ and it does not change. Having two sources carrying similar information leads to a more stable and coherent action.

Mind Reading with fMRI

From the Nature Editor's summary:

Recent functional magnetic resonance imaging (fMRI) studies have shown that, based on patterns of activity evoked by different categories of visual images, it is possible to deduce simple features in the visual scene, or to which category it belongs. Kay et al. take this approach a tantalizing step further. Their newly developed decoding method, based on quantitative receptive field models that characterize the relationship between visual stimuli and fMRI activity in early visual areas, can identify with high accuracy which specific natural image an observer saw, even for an image chosen at random from 1,000 distinct images. This prompts the thought that it may soon be possible to decode subjective perceptual experiences such as visual imagery and dreams, an idea previously restricted to the realm of science fiction.

The abstract from Kay et al., followed by one figure:

A challenging goal in neuroscience is to be able to read out, or decode, mental content from brain activity. Recent functional magnetic resonance imaging (fMRI) studies have decoded orientation, position, and object category from activity in visual cortex. However, these studies typically used relatively simple stimuli (for example, gratings) or images drawn from fixed categories (for example, faces, houses), and decoding was based on previous measurements of brain activity evoked by those same stimuli or categories. To overcome these limitations, here we develop a decoding method based on quantitative receptive-field models that characterize the relationship between visual stimuli and fMRI activity in early visual areas. These models describe the tuning of individual voxels for space, orientation and spatial frequency, and are estimated directly from responses evoked by natural images. We show that these receptive-field models make it possible to identify, from a large set of completely novel natural images, which specific image was seen by an observer. Identification is not a mere consequence of the retinotopic organization of visual areas; simpler receptive-field models that describe only spatial tuning yield much poorer identification performance. Our results suggest that it may soon be possible to reconstruct a picture of a person's visual experience from measurements of brain activity alone.


Figure Legend - The experiment consisted of two stages. In the first stage, model estimation, fMRI data were recorded while each subject viewed a large collection of natural images. These data were used to estimate a quantitative receptive-field model for each voxel. In the second stage, image identification, fMRI data were recorded while each subject viewed a collection of novel natural images. For each measurement of brain activity, we attempted to identify which specific image had been seen. This was accomplished by using the estimated receptive-field models to predict brain activity for a set of potential images and then selecting the image whose predicted activity most closely matches the measured activity.

The mind's eye in number space

From Loetscher et al., an interesting bit on how our subtle muscle movements correlate with counting operations - numbers and space:

Human subjects' answer to questions like “what number is halfway between 2 and 8” provides insights into spatial attention mechanisms involved in numerical processing. Here we show that mental numerical bisections are accompanied by a systematic pattern of horizontal eye movements: processing of a large number followed by a small number is accompanied with leftward eye movements, a tendency less pronounced or even reversed for the processing of a small number followed by a large number. The eyes thus appear to move along a left-to-right-oriented number line, indicating that shifts of attention in representational space are accompanied by an ocular motor orienting response. These results add to the growing evidence for a convergence of numerical processing, spatial attention, and movement planning in the parietal and frontal lobes. They also demonstrate the homologous relationship between our internal representations of numbers and space, and show that the concept of “number space” is more than a mere metaphor.

A hierarchy of temporal receptive windows in our brains

Here is the abstract from a fascinating study by Hasson et al. on how our visual system assembles time narratives - as during watching a movie - followed by part of one of the figures from the paper:

Real-world events unfold at different time scales and, therefore, cognitive and neuronal processes must likewise occur at different time scales. We present a novel procedure that identifies brain regions responsive to sensory information accumulated over different time scales. We measured functional magnetic resonance imaging activity while observers viewed silent films presented forward, backward, or piecewise-scrambled in time. Early visual areas (e.g., primary visual cortex and the motion-sensitive area MT+) exhibited high response reliability regardless of disruptions in temporal structure. In contrast, the reliability of responses in several higher brain areas, including the superior temporal sulcus (STS), precuneus, posterior lateral sulcus (LS), temporal parietal junction (TPJ), and frontal eye field (FEF), was affected by information accumulated over longer time scales. These regions showed highly reproducible responses for repeated forward, but not for backward or piecewise-scrambled presentations. Moreover, these regions exhibited marked differences in temporal characteristics, with LS, TPJ, and FEF responses depending on information accumulated over longer durations (~36 s) than STS and precuneus (~12 s). We conclude that, similar to the known cortical hierarchy of spatial receptive fields, there is a hierarchy of progressively longer temporal receptive windows in the human brain.


Figure- Maps are shown on inflated (top) and unfolded (bottom) left and right hemispheres. White outlines mark the main regions in which responses were not time reversible. Anatomical abbreviations: ITS, inferior temporal sulcus; LS, lateral sulcus; STS, superior temporal sulcus; TPJ, temporal parietal junction; CS, central sulcus; IPS, intraparietal sulcus. Several higher-order visual areas were functionally defined based on their responses to faces (red outlines), objects (blue outlines), and houses (green outlines). Functionally and anatomically defined cortical areas: V1, primary visual cortex; MT+, MT complex responsive to visual motion; PPA, parahippocampal place area; FFA, fusiform face area; LO, lateral occipital complex responsive to pictures of objects; STS-face, area in superior temporal sulcus responsive to faces.

The maturing architecture of the brain's default network

From Raichle and others in the St. Louis group, an interesting story on the development of the brain network we most likely use for introspective mental activity:

In recent years, the brain's "default network," a set of regions characterized by decreased neural activity during goal-oriented tasks, has generated a significant amount of interest, as well as controversy. Much of the discussion has focused on the relationship of these regions to a "default mode" of brain function. In early studies, investigators suggested that, the brain's default mode supports "self-referential" or "introspective" mental activity. Subsequently, regions of the default network have been more specifically related to the "internal narrative," the "autobiographical self," "stimulus independent thought," "mentalizing," and most recently "self-projection." However, the extant literature on the function of the default network is limited to adults, i.e., after the system has reached maturity. We hypothesized that further insight into the network's functioning could be achieved by characterizing its development. In the current study, we used resting-state functional connectivity MRI (rs-fcMRI) to characterize the development of the brain's default network. We found that the default regions are only sparsely functionally connected at early school age (7–9 years old); over development, these regions integrate into a cohesive, interconnected network.


Figure legend - (click on figure to enlarge). Voxelwise resting-state functional connectivity maps for a seed region (solid black circle) in mPFC (ventral: –3, 39, –2). (A) Qualitatively, the rs-fcMRI map for the mPFC (ventral) seed region reveals the commonly observed adult connectivity pattern of the default network. The connectivity map in children, however, significantly deviates from that of the adults. Functional connections with regions in the posterior cingulate and lateral parietal regions (highlighted with blue open circles) are present in the adults but absent in children. (B) These qualitative differences between children and adults are confirmed by the direct comparison (random effects) between adults and children. mPFC (ventral) functional connections with the posterior cingulate and lateral parietal regions are significantly stronger in adults than children.

Our motor adaptation as a process of reoptimization.

Because I'm a classical pianist and am continually trying to optimize the motor performance involved, I'm fascinated by articles like this one by Izawa et al. They oppose the common assumption that the goal of motor adaptation is to compensate for some perturbation by returning to a previous baseline condition assumed to be optimal. Here is their abstract:

Adaptation is sometimes viewed as a process in which the nervous system learns to predict and cancel effects of a novel environment, returning movements to near baseline (unperturbed) conditions. An alternate view is that cancellation is not the goal of adaptation. Rather, the goal is to maximize performance in that environment. If performance criteria are well defined, theory allows one to predict the reoptimized trajectory. For example, if velocity-dependent forces perturb the hand perpendicular to the direction of a reaching movement, the best reach plan is not a straight line but a curved path that appears to overcompensate for the forces. If this environment is stochastic (changing from trial to trial), the reoptimized plan should take into account this uncertainty, removing the overcompensation. If the stochastic environment is zero-mean, peak velocities should increase to allow for more time to approach the target. Finally, if one is reaching through a via-point, the optimum plan in a zero-mean deterministic environment is a smooth movement but in a zero-mean stochastic environment is a segmented movement. We observed all of these tendencies in how people adapt to novel environments. Therefore, motor control in a novel environment is not a process of perturbation cancellation. Rather, the process resembles reoptimization: through practice in the novel environment, we learn internal models that predict sensory consequences of motor commands. Through reward-based optimization, we use the internal model to search for a better movement plan to minimize implicit motor costs and maximize rewards.

Relativity of space, time and magnitude representation in our brains

Here are some simple and elegant experiments that shows how relativistic our time sense is. Our two cerebral hemispheres expand (right hemisphere) or contract (left hemisphere) time perception when acting alone, and then let magnitude cues in the stimulus influence perceived time when acting together. Vicario et al. investigated whether duration judgments of digit visual stimuli were biased depending on the side of space where the stimuli were presented (i.e. to which hemisphere) and on the magnitude of the stimulus itself:

Different groups of healthy subjects performed duration judgment tasks on various types of visual stimuli. In the first two experiments visual stimuli were constituted by digit pairs (1 and 9), presented in the centre of the screen or in the right and left space. In a third experiment visual stimuli were constituted by black circles. The duration of the reference stimulus was fixed at 300 ms. Subjects had to indicate the relative duration of the test stimulus compared with the reference one. The main results showed that, regardless of digit magnitude, duration of stimuli presented in the left hemispace is underestimated and that of stimuli presented in the right hemispace is overestimated. On the other hand, in midline position, duration judgments are affected by the numerical magnitude of the presented stimulus, with time underestimation of stimuli of low magnitude and time overestimation of stimuli of high magnitude. These results argue for the presence of strict interactions between space, time and magnitude representation on the human brain.

Influence of language on brain activity underlying perceptual decisions

Following up on my Feb. 22 post on the same topic, I pass on the abstract of work by Tan et al., showing that language-processing areas of the brain are directly involved in visual perceptual decisions:

Well over half a century ago, Benjamin Lee Whorf [Carroll JB (1956) Language, Thought, and Reality: Selected Writings of Benjamin Lee Whorf (MIT Press, Cambridge, MA)] proposed that language affects perception and thought and is used to segment nature, a hypothesis that has since been tested by linguistic and behavioral studies. Although clear Whorfian effects have been found, it has not yet been demonstrated that language influences brain activity associated with perception and/or immediate postperceptual processes (referred hereafter as "perceptual decision"). Here, by using functional magnetic resonance imaging, we show that brain regions mediating language processes participate in neural networks activated by perceptual decision. When subjects performed a perceptual discrimination task on easy-to-name and hard-to-name colored squares, largely overlapping cortical regions were identified, which included areas of the occipital cortex critical for color vision and regions in the bilateral frontal gyrus. Crucially, however, in comparison with hard-to-name colored squares, perceptual discrimination of easy-to-name colors evoked stronger activation in the left posterior superior temporal gyrus and inferior parietal lobule, two regions responsible for word-finding processes, as demonstrated by a localizer experiment that uses an explicit color patch naming task. This finding suggests that the language-processing areas of the brain are directly involved in visual perceptual decision, thus providing neuroimaging support for the Whorf hypothesis.

Figure legend (Click on figure to enlarge it). Brain activations elicited by color perception and explicit color naming. (A and B) Areas showing significant activation during perceptual discrimination of easy-to-name colors in comparison with perceptual discrimination of hard-to-name colors. A and B are lateral view and axial sections, respectively. Two regions of greatest interest are the left posterior superior temporal gyrus (BA 22; x = –57, y = –38, z = 18) and the left inferior parietal lobule (BA 40; x = –61, y = –32, z = 27). (C and D) Percentage BOLD signal change (± SEM) at voxels of maximal difference between the two color-discrimination conditions in the two regions of interest. (E and F) Areas showing significant activation in explicit color naming against color word naming as baseline. E and F are lateral view and axial sections, respectively. The left posterior superior temporal gyrus and the left inferior parietal lobule are critically engaged by the color naming task.

The brain and emotion-laden images: two pathways

A collaborative study has considered several models that might explain why our behavior can be rapidly influenced by an emotional stimulus (a snake like shape that we jump away from) before the stimulus has been fully processed (and we realize that it is a coil of rope). Information influences action before perception is complete. The data can only be accounted for by a two-pathway architecture by which emotional visual information proceeds more directly via one pathway to the amygdala (and thus influences action) and at the same time more slowly by the second conventional visual pathway that establishes the perception of the actual nature of the stimulus. I'm showing here the abstract and then the basic figure describing the models.

Visual attention can be driven by the affective significance of visual stimuli before full-fledged processing of the stimuli. Two kinds of models have been proposed to explain this phenomenon: models involving sequential processing along the ventral visual stream, with secondary feedback from emotion-related structures ("two-stage models"); and models including additional short-cut pathways directly reaching the emotion-related structures ("two-pathway models"). We tested which type of model would best predict real magnetoencephalographic responses in subjects presented with arousing visual stimuli, using realistic models of large-scale cerebral architecture and neural biophysics. The results strongly support a "two-pathway" hypothesis. Both standard models including the retinotectal pathway and nonstandard models including cortical–cortical long-range fasciculi appear plausible.

Tested models. (Click on image to enlarge) a, Basic components of the generic model, including all the possible types of connections used in this report, within and between two connected regions. Top, Cortical regions are modeled as three layered columns with three types of neuronal populations (pyramidal, excitatory spiny, and inhibitory interneurons), connected through intrinsic and extrinsic (feedforward and backward) connections. Bottom, The dynamics is mathematically expressed at the level of neural populations and is defined by nonlinear differential equations in which the change of state of each unit dxi/dt depends on its current state xi(t); thalamic inputs ui(t); average firing rate of afferents S(xj(t – {delta}ij)); transmission delays {delta}ij; forward, backward, and intrinsic effective connectivity matrices CF, CB, Ci, and other parameters. The MEG signal M is assumed to be related to the local average current density x generated by pyramidal populations through a linear forward model M = GX. b, Lateral, mesial, and ventral views of the mapping of the regions of interest common to all models on a reference cortical tessellation [for color code, see c (top row)]. c, Schematic representation of the architecture of the tested models. All the models share the same basic layout (see text). Null model, Simple feedforward model. Model 1, Adjunction of connectivity modulation. Model 2 (2-stage model), Adjunction of local feedbacks. Model 3 (2-stage model), Adjunction of long-range feedbacks from structures of the AAS (anterior affective system). Model 4 (2-pathway model), Adjunction of a direct subcortical retinotectal short-cut pathway to the AAS. Model 5 (2-pathway model), Alternative short-cut pathways to the AAS via the inferior longitudinal and frontal–occipital fasciculi. Model 6 (2-pathway model), Combination of models 4 and 5. Orange circles, "Synapses" at which modulation by emotional competence of the stimuli is implemented.

Awaress and attention: different brain processes

Most of the proposed neural correlates of visual awareness do not explicitly distinguish top-down attention from awareness per se. However, several authors have started to point at the need to disambiguate visual awareness and spatial attention. Experimental evidence supporting their possible neural dissociation has remained sparse. Such evidence is now provided by a nice piece of work from Wyart and Tallon-Baudry:

To what extent does what we consciously see depend on where we attend to? Psychologists have long stressed the tight relationship between visual awareness and spatial attention at the behavioral level. However, the amount of overlap between their neural correlates remains a matter of debate. We recorded magnetoencephalographic signals while human subjects attended toward or away from faint stimuli that were reported as consciously seen only half of the time. Visually identical stimuli could thus be attended or not and consciously seen or not. Although attended stimuli were consciously seen slightly more often than unattended ones, the factorial analysis of stimulus-induced oscillatory brain activity revealed distinct and independent neural correlates of visual awareness and spatial attention at different frequencies in the gamma range (30–150 Hz). Whether attended or not, consciously seen stimuli induced increased mid-frequency gamma-band activity over the contralateral visual cortex, whereas spatial attention modulated high-frequency gamma-band activity in response to both consciously seen and unseen stimuli. A parametric analysis of the data at the single-trial level confirmed that the awareness-related mid-frequency activity drove the seen–unseen decision but also revealed a small influence of the attention-related high-frequency activity on the decision. These results suggest that subjective visual experience is shaped by the cumulative contribution of two processes operating independently at the neural level, one reflecting visual awareness per se and the other reflecting spatial attention.

Watching yourself during a brain stroke...

This widely circulating video has some fascinating insights into the experience of having a stroke. Jill Bolte Taylor gives an very simplified description of left versus right hemisphere function and then describes the consequences of a hemmorage in her left hemisphere that formed a large clot pressing against the language area. She watched a flickering back and forth between having a self with thoughts and a la-la land or nirvana of pure awareness as she gradually lost motor and sensory control :

More on Brain Enhancement

Have a look at Benedict Carey's article, "Brain Enhancement Is Wrong, Right?," in the NY Times Week in Review of 3/9/08. It continues the topic of using performance enhancing drugs, following up on a Nature article that I mentioned in my Feb. 1 post on the same subject. By the way, I have been meaning to point you to Chris Chatham's excellent post on how to use caffeine properly, obtaining effects on cognitive performance equivalent to those of modifanil. Here are some clips from the Carey article:

...two Cambridge University researchers reported that about a dozen of their colleagues had admitted to regular use of prescription drugs like Adderall, a stimulant, and Provigil, which promotes wakefulness, to improve their academic performance. The former is approved to treat attention deficit disorder, the latter narcolepsy, and both are considered more effective, and more widely available, than the drugs circulating in dorms a generation ago.

Francis Fukuyama raises the broader issue of performance enhancement: “The original purpose of medicine is to heal the sick, not turn healthy people into gods.” He and others point out that increased use of such drugs could raise the standard of what is considered “normal” performance and widen the gap between those who have access to the medications and those who don’t — and even erode the relationship between struggle and the building of character.

People already use legal performance enhancers, he said, from high-octane cafe Americanos to the beta-blockers taken by musicians to ease stage fright, to antidepressants to improve mood. “So the question with all of these things is, Is this enhancement, or a matter of removing the cloud over our better selves?”.

“You can imagine a scenario in the future, when you’re applying for a job, and the employer says, ‘Sure, you’ve got the talent for this, but we require you to take Adderall.’ Now, maybe you do start to care about the ethical implications.”

Your pupils reveal shifts in your perception

Here is an interesting nugget from Christof Koch's laboratory at Cal Tech. When we look at an ambiguous image such as the Necker Cube or the duck/rabbit shown here, our perception switches back and forth between the alternatives.


It turns out that our pupil diameter increases just before the perceptual switch, and predicts its duration. Here is their abstract:

During sustained viewing of an ambiguous stimulus, an individual's perceptual experience will generally switch between the different possible alternatives rather than stay fixed on one interpretation (perceptual rivalry). Here, we measured pupil diameter while subjects viewed different ambiguous visual and auditory stimuli. For all stimuli tested, pupil diameter increased just before the reported perceptual switch and the relative amount of dilation before this switch was a significant predictor of the subsequent duration of perceptual stability. These results could not be explained by blink or eye-movement effects, the motor response or stimulus driven changes in retinal input. Because pupil dilation reflects levels of norepinephrine (NE) released from the locus coeruleus (LC), we interpret these results as suggestive that the LC–NE complex may play the same role in perceptual selection as in behavioral decision making.

Bright light and good moods...

We are more agreeable when the light is brighter: here is the abstract, and one figure, from "Exposure to bright light is associated with positive social interaction and good mood over short time periods: A naturalistic study in mildly seasonal people" published in the Journal of Psychology:

Bright light is used to treat winter depression and might also have positive effects on mood in some healthy individuals. We examined possible links between bright light exposure and social interaction using naturalistic data. For 20 days in winter and/or summer, 48 mildly seasonal healthy individuals wore a light meter at the wrist and recorded in real-time their behaviours, mood, and perceptions of others during social interactions. Possible short-term effects of bright light were examined using the number of minutes, within any given morning, afternoon or evening, that people were exposed to light exceeding 1000 lux (average: 19.6 min). Social interactions were labelled as having occurred under conditions of no, low or high bright light exposure. Independent of season, day, time, and location, participants reported less quarrelsome behaviours, more agreeable behaviours and better mood when exposed to high but not low levels of bright light. Given that the effects were seen only when exposure levels were above average, a minimum level of bright light may be necessary for its positive effects to occur. Daily exposure levels were generally low in both winter and summer. Spending more time outdoors and improving indoor lighting may help optimize everyday social behaviour and mood across seasons in people with mild seasonality.

Figure - Quarrelsome behaviours (a) and agreeable behaviours (b) during time periods of no, low, or high levels of bright light exposure. Values are expressed as estimated least squares means of ipsatized frequencies, multiplied by a factor 100. Error bars represent standard errors of the mean. (* Significantly different from social interactions with low bright light exposure.)

Languages shape the nuts and bolts of our perception.

The debate over whether language nudges the way we actually see the world is being resolved, and what has been the prevailing dogma - that basic parts of perception are too low-level, too hard-wired, too constrained by the constants of physics and physiology to be affected by language - is breaking down. Lera Boroditsky at Standford comments on this.

I used to think that languages and cultures shape the ways we think. I suspected they shaped they ways we reason and interpret information. But I didn't think languages could shape the nuts and bolts of perception, the way we actually see the world. That part of cognition seemed too low-level, too hard-wired, too constrained by the constants of physics and physiology to be affected by language.

Then studies started coming out claiming to find cross-linguistic differences in color memory. For example, it was shown that if your language makes a distinction between blue and green (as in English), then you're less likely to confuse a blue color chip for a green one in memory. In a study like this you would see a color chip, it would then be taken away, and then after a delay you would have to decide whether another color chip was identical to the one you saw or not.

Of course, showing that language plays a role in memory is different than showing that it plays a role in perception. Things often get confused in memory and it's not surprising that people may rely on information available in language as a second resort. But it doesn't mean that speakers of different languages actually see the colors differently as they are looking at them. I thought that if you made a task where people could see all the colors as they were making their decisions, then there wouldn't be any cross-linguistic differences.

I was so sure of the fact that language couldn't shape perception that I went ahead and designed a set of experiments to demonstrate this. In my lab we jokingly referred to this line of work as "Operation Perceptual Freedom." Our mission: to free perception from the corrupting influences of language.

We did one experiment after another, and each time to my surprise and annoyance, we found consistent cross-linguistic differences. They were there even when people could see all the colors at the same time when making their decisions. They were there even when people had to make objective perceptual judgments. They were there when no language was involved or necessary in the task at all. They were there when people had to reply very quickly. We just kept seeing them over and over again, and the only way to get the cross-linguistic differences to go away was to disrupt the language system. If we stopped people from being able to fluently access their language, then the cross-linguistic differences in perception went away.

I set out to show that language didn't affect perception, but I found exactly the opposite. It turns out that languages meddle in very low-level aspects of perception, and without our knowledge or consent shape the very nuts and bolts of how we see the world.

Watching waves of activity sweep across the brain

This is sensory physiology in the age of YouTube. Peterson and colleagues have used a voltage sensitive dye technique to watch the wave of first sensory area and then motor area excitation that is caused by a tiny deflection of a face whisker of a mouse:

Single brief whisker deflections evoked highly distributed depolarizing cortical sensory responses, which began in the primary somatosensory barrel cortex and subsequently excited the whisker motor cortex. The spread of sensory information to motor cortex was dynamically regulated by behavior and correlated with the generation of sensory-evoked whisker movement. Sensory processing in motor cortex may therefore contribute significantly to active tactile sensory perception.

The video shows the response when a mouses whisker touches an edge:

The movement of the C2 whisker was filmed with a high-speed camera at 500 Hz in an awake behaving mouse during an active touch sequence. Sensorimotor cortex was simultaneously imaged with VSD. At the time indicated by the vertical dotted line, the whisker contacts the object evoking a spreading sensorimotor response, first in S1 and subsequently in M1. The single trial imaging of cortical activity and the behavioral filming are matched frame-by-frame, synchronized through TTL pulses.

Oliver Sachs on Migraines

An interesting article on Migraines by Oliver Sachs in the Op-Extra section of The New York Times, focusing on the geometric hallucinations they so often evoke.

...when I first saw photographs of the Alhambra, with its intricate geometric mosaics, I started to wonder whether what I had taken to be a personal experience and resonance might in fact be part of a larger whole, whether certain basic forms of geometric art, going back for tens of thousands of years, might also reflect the external expression of universal experiences. Migraine-like patterns, so to speak, are seen not only in Islamic art, but in classical and medieval motifs, in Zapotec architecture, in the bark paintings of Aboriginal artists in Australia, in Acoma pottery, in Swazi basketry — in virtually every culture. There seems to have been, throughout human history, a need to externalize, to make art from, these internal experiences, from the decorative motifs of prehistoric cave paintings to the psychedelic art of the 1960s. Do the arabesques in our own minds, built into our own brain organization, provide us with our first intimations of geometry, of formal beauty?

Whether or not this is the case, there is an increasing feeling among neuroscientists that self-organizing activity in vast populations of visual neurons is a prerequisite of visual perception — that this is how seeing begins. Spontaneous self-organization is not restricted to living systems — one may see it equally in the formation of snow crystals, in the roilings and eddies of turbulent water, in certain oscillating chemical reactions. Here, too, self-organization can produce geometries and patterns in space and time, very similar to what one may see in a migraine aura. In this sense, the geometrical hallucinations of migraine allow us to experience in ourselves not only a universal of neural functioning, but a universal of nature itself.