Listening with your visual cortex.

We experience our environment through simultaneous stimulation of several sensory channels. Watching a movie is usually a visual and auditory experience. This integration from different sensory modalities helps with stimulus detection and discrimination in noisy environments. A traditional views of brain organization has postulated strict parceling into unisensory and and then multisensory cortical levels. Romei et al. have now shown in humans that auditory information goes directly to the primary visual cortex, before higher levels of integration.

When subjects are instructed to detect simple stimuli (a briefly presented pure tone, a small white disk, or a combination of the two), and their reaction times (RTs) are measured, reaction RTs are significantly better for the audio-visual (AV) condition than for both unimodal conditions, indicating a behavioral facilitation effect for stimuli presented simultaneously in both modalities. Romei et al. gave brief trans-cranial magnetic stimultion (TMS) to occipital poles of the subjects' heads. TMS effects over visual cortex in a timeframe from 60 to 75 ms after sensory stimulus onset would suggest an interaction with feedforward processes, whereas later effects might be caused by feedback from higher cortical regions. Thus, varying the delay from 30 to 150 ms between TMS and the preceding sensory stimulation in different sensory modalities enabled them to determine the processing type (feedforward or feedback), as well as the critical timeframe of visual cortex involvement in stimulus processing.

Relative to TMS over a control site, reactions times (RTs) to unisensory visual stimuli were prolonged by TMS at 60–75 ms poststimulus onset (visual suppression effect), confirming stimulation of functional visual cortex. Conversely, RTs to unisensory auditory stimuli were significantly shortened when visual cortex was stimulated by TMS at the same delays (beneficial interaction effect of auditory stimulation and occipital TMS). No TMS-effect on RTs was observed for AV stimulation. A follow-up experiment showed that auditory input enhances excitability within visual cortex itself over a similarly early time-window (75–120 ms).

Face perception after no experience of faces

This work really nails down the fact that face processing is a special perceptual process and is organized as such at birth, as contrasted with having its origin in a more general-purpose perceptual system that becomes specialized after frequent visual experiences. Sugita has studied face perception in monkeys reared with no exposure to faces. Here is his abstract, and one figure from the paper:

Infant monkeys were reared with no exposure to any faces for 6–24 months. Before being allowed to see a face, the monkeys showed a preference for human and monkey faces in photographs, and they discriminated human faces as well as monkey faces. After the deprivation period, the monkeys were exposed first to either human or monkey faces for a month. Soon after, the monkeys selectively discriminated the exposed species of face and showed a marked difficulty in regaining the ability to discriminate the other nonexposed species of face. These results indicate the existence of an experience-independent ability for face processing as well as an apparent sensitive period during which a broad but flexible face prototype develops into a concrete one for efficient processing of familiar faces.

Figure: An infant monkey and her living circumstance. An infant monkey and a caregiver with (A) and without (B) a facemask. Both photos were taken after the face-deprivation period. (C) Toys placed in the monkey's home cage. (D) Decorations provided around the home cage.

We Differ More Than We Thought

This essay by Mark Pagel is worth passing on in its entirety:

The last thirty to forty years of social science has brought an overbearing censorship to the way we are allowed to think and talk about the diversity of people on Earth. People of Siberian descent, New Guinean Highlanders, those from the Indian sub-continent, Caucasians, Australian aborigines, Polynesians, Africans — we are, officially, all the same: there are no races.

Flawed as the old ideas about race are, modern genomic studies reveal a surprising, compelling and different picture of human genetic diversity. We are on average about 99.5% similar to each other genetically. This is a new figure, down from the previous estimate of 99.9%. To put what may seem like miniscule differences in perspective, we are somewhere around 98.5% similar, maybe more, to chimpanzees, our nearest evolutionary relatives.

The new figure for us, then, is significant. It derives from among other things, many small genetic differences that have emerged from studies that compare human populations. Some confer the ability among adults to digest milk, others to withstand equatorial sun, others yet confer differences in body shape or size, resistance to particular diseases, tolerance to hot or cold, how many offspring a female might eventually produce, and even the production of endorphins — those internal opiate-like compounds.

We also differ by surprising amounts in the numbers of copies of some genes we have. Modern humans spread out of Africa only within the last 60-70,000 years, little more than the blink of an eye when stacked against the 6 million or so years that separate us from our Great Ape ancestors. The genetic differences amongst us reveal a species with a propensity to form small and relatively isolated groups on which natural selection has often acted strongly to promote genetic adaptations to particular environments.

We differ genetically more than we thought, but we should have expected this: how else but through isolation can we explain a single species that speaks at least 7,000 mutually unintelligible languages around the World?

What this all means is that, like it or not, there may be many genetic differences among human populations — including differences that may even correspond to old categories of 'race' — that are real differences in the sense of making one group better than another at responding to some particular environmental problem. This in no way says one group is in general 'superior' to another, or that one group should be preferred over another. But it warns us that we must be prepared to discuss genetic differences among human populations.

Please Clap, Talk or Shout at Any Time

Bernard Holland reviews Kenneth Hamilton's book, “After the Golden Age,” a detailed reflection on concert behavior in the 19th and early 20th centuries published recently by Oxford University Press. Fascinating bits of information about a bygone era before our current time, when

Concertgoers like you and me have become part police officer, part public offender. We prosecute the shuffled foot or rattled program, the errant whisper or misplaced cough. We tense at the end of a movement, fearful that one of the unwashed will begin to clap, bringing shame on us all. How serious we look, and how absurd we are.

A number of fascinating facts:

...the silence at a London performance of Liszt’s “Dante” Symphony represented not rapt attention but audience distaste.
...hardly anybody played more than one movement of a Beethoven sonata at a time.
...Audience participation was taken for granted in the 1840s. The pianist Alexander Dreyschock was criticized for playing “so loud that it made it difficult for the ladies to talk,”

...Concerts were different back then. Liszt could get away with the radical idea of “one man, one recital,” but musical events were usually variety shows in the manner of vaudeville. The star pianist or violinist was just an occasionally recurring act in a parade of singers, orchestra players, quartets and trios. When Liszt did his solo acts, there was none of the march-on, march-off stage ritual of today. Liszt greeted patrons at the door, mingled in the audience and schmoozed with friend and stranger alike.

...Whole recitals also took place between acts of an opera or movements of a symphony. When Chopin played his E minor Piano Concerto in Warsaw in 1830, other pieces were inserted between the first two movements. Perhaps the most celebrated such interruption was at the 1806 premiere of Beethoven’s Violin Concerto in Vienna, where the soloist thrilled listeners by playing his violin upside down and on one string.

Regret

How do we feel about alternative versions of ourselves - lost possible selves, or the person we might have been? Benedict Carey writes a nice piece on this question. A few clips:

...Over the past decade and a half, psychologists have studied how regrets — large and small, recent and distant — affect people’s mental well-being. They have shown, convincingly though not surprisingly, that ruminating on paths not taken is an emotionally corrosive exercise. The common wisdom about regret — that what hurts the most is not what you did but what you didn’t do — also appears to be true, at least in the long run.

...young adults who scored high on measures of psychological well-being tended to think of regretted decisions as all their own — perhaps because they still had time to change course. By contrast, older people who scored highly tended to share blame for their regretted decisions. “I tried to reach out to him, but the effort wasn’t returned.”

...those who are able to talk or write about this lost future without sinking into despair or losing hope tend to have developed another quality, called complexity...an ability to incorporate various points of view into a recollection, to vividly describe the circumstances, context and other dimensions...that this knack for self-evaluation develops over time; it is a learned ability.

...therapists have long known the value of seeing regretted choices in the context of what has been gained as well as lost.

...the perspective from which people remember slights or mistakes can affect the memories’ emotional impact... reimagining painful scenes from a third-person point of view, as if seeing oneself in a movie, blunts their emotional sting and facilitates ... clearheaded self-perception.

Compensatory neural plasticity in aging human brains.

Recent imaging studies have shown that seniors exhibit stronger brain activation than younger controls during the execution of various motor tasks. Old subjects activate the same regions as their younger counterparts, but to a larger extent, and they also activate additional regions that are not observed in the young subjects.

Heuninckx et al. examine the underlying neural mechanisms of this "overactivation" by determining whether it reflects compensation for various neural/behavioral deficits (e.g., neurodegeneration, attentional problems, reduction in sensory function, etc.) or whether it is due to de-differentiation (a generalized nonfunctional spread of activity attributable to deficits in neurotransmission, which in turn causes a decrease in the signal-to-noise ratio in neural firing and a loss of neural specialization). They compared brain activity in 24 older adults and 11 young controls during the performance of rhythmical hand–foot coordination tasks, whereby both limbs moved either in the same (iso-directional) or in the opposite (non-isodirectional, NONISODIR in the figure below) direction. Previous behavioral work had shown convincingly that the non-isodirectional pattern is more difficult and is produced with lower accuracy and stability than the iso-directional pattern. Activation in dedicated brain regions was correlated with motor performance in the elderly. According to the compensation hypothesis, the underlying rationale was that the over-activation would be larger in good than in poor motor performers, with the effect being more pronounced in more (non-isodirectional) than less (iso-directional) demanding coordination tasks. Conversely, the de-differentiation hypothesis assumed overactivation to be larger in poor than in successful motor performers because of nonfunctional neural irradiation. Thus, positive correlations between brain activation and motor performance were considered to reflect compensation, and negative correlations were considered to reflect de-differentiation.

They found that that coordination resulted in activation of classical motor coordination regions and also higher-level sensorimotor and frontal regions in the elderly. A positive correlation between activation level in these latter regions and motor performance was observed. This performance enhancing additional recruitment is consistent with the compensation hypothesis and reflects neuroplasticity at the systems level in the aging brain.


Figure: (Click to enlarge). Statistical parametric maps representing significantly larger activation in the old compared with the young group during the NONISODIR coordination mode, resulting from the following contrast: (NONISODIR – rest)old versus (NONISODIR – rest)young. L, Left hemisphere; R, right hemisphere. White arrows indicate brain regions that exhibit a significant correlation between brain activity level and coordination performance, as identified by a whole-brain multiple regression analysis. The graphics display each subject's BOLD response with respect to the within-cluster peak activation as a function of the inverse of the phase error (1/AE), with the younger subjects in blue and the older subjects in red.

What have you changed your mind about?

The Edge.org Annual Question for 2008, addressed to a select group of their choice of the intellectual elite, is "What have you changed your mind about? Why?" (I've done blog postings on the responses to questions of the two previous years: "What is your dangerous idea?" and "What are you optimistic about? Why?"

I started to do thumbnail summaries of the responses I thought worth passing on to you, but found that most were not very succinct, and sufficiently diffuse to make brief summary difficult. Then pack much less punch than the 'dangerous idea' responses. I recommend that you scroll through the responses yourself. I may focus on a few of them in subsequent posts.

Drunken flies get hypersexual - and gay

Sound familiar? Reminds me of similar behaviors after University of Wisconsin football games, when drunken guys who could not find an appropriate female object would go ahead with what was available - other guys. This news item by Heidi Ledford in Nature describes experiments by Lee et al. that:

...tested the effects of chronic alcohol exposure on sexual behaviour in the fruitfly Drosophila melanogaster. The researchers noted that male flies repeatedly exposed to ethanol vapour became less discriminate in their mate selection. The buzzed flies often courted fellow males, pursuing them around the cage while serenading with a traditional fruitfly courtship song played on vibrating wings.


[Figure: Love Chain, male fruit flies chase each other in a circle] Eventually, the lusty flies devolve into a courting frenzy. “You get a chain of males chasing each other,” says Heberlein, who was not associated with the study but has observed similar behaviour in her own unpublished work. In contrast, alcohol had little effect on mating in female fruitflies, which normally do not court their mates.

The findings suggest that the flies do not fundamentally change their sexual orientation, but rather get over-sexed. “Multiple alcohol exposures makes them essentially hypersexual,” says Heberlein. The mind-dulling effects of alcohol might also make it more of a challenge for male fruitflies to distinguish the gender of other flies in the crowd.

Because of the genetic tools available, fruitflies might be a good model system for probing the idea, suggested for humans, that the neurotransmitter dopamine is a link between sex and alcohol.

Love hangover - the sex peptide

A male, after copulation, has a particular interest in seeing that the female involved ceases further sexual activity that might dilute his genetic contribution. It turns out that male fruitflies don't have to stand by and guard their transferred genetic material — a sex peptide in their semen will do the job. This peptide leads to increased egg-laying by the mated female and behavioural changes that reduce the likelihood of her re-mating. Yapici et al. have now identified the receptor protein for this peptide. It functions in a subset of neurons implicated in other sex-related behaviors. The receptor is highly conserved across insect species, raising the possibility that it could be targeted to disrupt reproduction in insect pests or host-seeking behaviour in disease vectors. (There appears to be no evidence for such a mechanism in primates and humans!).

More on laughing rats...and human chanting?

This is a sequel to my March 20 and June 18, 2007, posts on laughing rats. Rats use ultrasonic communication, with 50-kHz vocalizations indicating an animal's positive subjective state. Wöhr and Schwarting now show that show that 50-kHz signals (either natural 50-kHz calls, which had been previously recorded from other rats, or artificial sine wave stimuli, which were identical to these calls with respect to peak frequency, call length and temporal appearance) can induce approach behaviors. The effect is more pronounced in juvenile rats. It is commonly assumed that humans have lost this mechanism, but I wonder if the powerful bonding emotions induced in groups of humans doing very low frequency vocal chants, which surely have harmonics in the 50-mHz range, might be a evolutionary derivative of this early mammalian behavior . Here are several Tibetan master chants offered by the free sound project. Do they chill you out?

The value of believing in free will.

Vohs and Schooler do an interesting experiment in which they ask whether believing in free will versus determinism influences moral behavior. I have free access only to the abstract of the article, so can not spell out the details of the experiments. Here is that abstract:

Does moral behavior draw on a belief in free will? Two experiments examined whether inducing participants to believe that human behavior is predetermined would encourage cheating. In Experiment 1, participants read either text that encouraged a belief in determinism (i.e., that portrayed behavior as the consequence of environmental and genetic factors) or neutral text. Exposure to the deterministic message increased cheating on a task in which participants could passively allow a flawed computer program to reveal answers to mathematical problems that they had been instructed to solve themselves. Moreover, increased cheating behavior was mediated by decreased belief in free will. In Experiment 2, participants who read deterministic statements cheated by overpaying themselves for performance on a cognitive task; participants who read statements endorsing free will did not. These findings suggest that the debate over free will has societal, as well as scientific and theoretical, implications.

A YouTube for ideas......

You might enjoy checking out this article by Tim Arango on a new website, Big Think, which appears to be a sort of combination of YouTube and Facebook for intellectuals.

Why can't we perform perfectly?

Some fascinating experiments by Tumer and Brainar on songbirds inform me on why I am not able to perform a completely learned and exhaustively practiced piano piece the same way each time I bang it out.... from the Nature Editor's review of their article:

Why is it that even the best-trained athletes and musicians cannot perform perfectly? One thought is that residual variability in performance is 'noise' that reflects fundamental limits on our ability to control our movements. Experiments using the exceptionally well-rehearsed songs of adult songbirds as a model point to an alternative explanation. Computerized monitoring of the apparently stereotyped songs of adult Bengalese finches revealed minuscule variations in performance. When the birds were given corrections each time the song varied beyond a certain limit, they rapidly learned to adapt their vocalizations. The implication is that once learned, songs can be maintained despite subtle changes to the vocal system due to factors such as ageing. So behavioural 'noise', rather than simply being a nuisance, may reflect experimentation by the nervous system to refine performance.

The abstract from Rumer and Brainar:

Significant trial-by-trial variation persists even in the most practiced skills. One prevalent view is that such variation is simply 'noise' that the nervous system is unable to control or that remains below threshold for behavioural relevance. An alternative hypothesis is that such variation enables trial-and-error learning, in which the motor system generates variation and differentially retains behaviours that give rise to better outcomes. Here we test the latter possibility for adult bengalese finch song. Adult birdsong is a complex, learned motor skill that is produced in a highly stereotyped fashion from one rendition to the next. Nevertheless, there is subtle trial-by-trial variation even in stable, 'crystallized' adult song. We used a computerized system to monitor small natural variations in the pitch of targeted song elements and deliver real-time auditory disruption to a subset of those variations. Birds rapidly shifted the pitch of their vocalizations in an adaptive fashion to avoid disruption. These vocal changes were precisely restricted to the targeted features of song. Hence, birds were able to learn effectively by associating small variations in their vocal behaviour with differential outcomes. Such a process could help to maintain stable, learned song despite changes to the vocal control system arising from ageing or injury. More generally, our results suggest that residual variability in well learned skills is not entirely noise but rather reflects meaningful motor exploration that can support continuous learning and optimization of performance.

Hope worse than Hopelessness

This short piece by Marina Krakovsky from the NY Times:

People often display a remarkable ability to adapt to adversity, bouncing back to their usual levels of happiness despite extreme hardships. But people don’t always rebound, and scientists have long wondered what factors might account for the difference. In a talk at Harvard in September, a team of researchers suggested that one obstacle to emotional recovery, oddly enough, is hope — the belief that your current hardship is temporary.

From the beginning, the investigators suspected that hope might sometimes be counterproductive: prisoners with life sentences but with the possibility of parole adapt less well to prison life, for example, than prisoners with life sentences without the possibility of parole. But the researchers sought another empirical test. Their choice: Colostomy patients. The research team, led by Peter Ubel, a physician at the University of Michigan, tracked people who had portions of their colons removed or bypassed, such that the patients couldn’t defecate normally. The condition is extremely unpleasant and leads many people to say they’d rather be dead, Ubel reports. But a colostomy isn’t always permanent. Some patients are likely to heal and have their bowels reconnected. Whether your colostomy is permanent depends on your condition, but were it up to the patient to choose, “almost anybody would choose temporary over permanent,” Ubel says.

So it’s surprising that the permanent-colostomy patients ended up happier six months after the operation than the temporary group, whose members were still holding out hope. Patients with a temporary colostomy experienced a significant drop in life satisfaction versus patients in the permanent group.


It might seem strange that patients who are better off objectively were less satisfied with their lives, yet the finding makes sense: “If your condition is temporary,” Ubel explains, “you’re thinking, I can’t wait until I get rid of this.” Ubel says thoughts like these keep you from moving on with your life and focusing on the many good things that remain.

Clutter - more in the brain than in the house...

Parker-Pope offers a brief essay on the "clutter problem," suggesting that the problem in many cases is not a house problem but a person problem.

Excessive clutter and disorganization are often symptoms of a bigger health problem...At its most extreme, chronic disorganization is called hoarding...David F. Tolin, director of the anxiety disorders center at the Institute of Living in Hartford and an adjunct associate professor of psychiatry at Yale...recently studied compulsive hoarders using brain-scan technology. While in the scanner, hoarders looked at various possessions and made decisions about whether to keep them or throw them away. The items were shredded in front of them, so they knew the decision was irreversible. When a hoarder was making decisions about throwing away items, the researchers saw increased activity in the orbitofrontal cortex, a part of the brain involved in decision-making and planning...people who didn’t hoard showed no extra brain activity.

The article continues with a discussion of holding on to excess 'stuff' and being overweight. In several cases therapists have noted a correlation between reducing clutter and weight loss.

Cultural Influences on Neural Substrates of Attentional Control

The abstract from Hedden et al. of the article with the title of this post (in Psychological Science, Volume 19, pp 12-17, 2008). I thought it was interesting enough to mention, though I don't have access to the full text, so can't determine exactly what is meant by culturally preferred and non-preferred judgements:

Behavioral research has shown that people from Western cultural contexts perform better on tasks emphasizing independent (absolute) dimensions than on tasks emphasizing interdependent (relative) dimensions, whereas the reverse is true for people from East Asian contexts. We assessed functional magnetic resonance imaging responses during performance of simple visuospatial tasks in which participants made absolute judgments (ignoring visual context) or relative judgments (taking visual context into account). In each group, activation in frontal and parietal brain regions known to be associated with attentional control was greater during culturally nonpreferred judgments than during culturally preferred judgments. Also, within each group, activation differences in these regions correlated strongly with scores on questionnaires measuring individual differences in culture-typical identity. Thus, the cultural background of an individual and the degree to which the individual endorses cultural values moderate activation in brain networks engaged during even simple visual and attentional tasks.

A science debate for presidential candidates?

A note for this day of the Iowa presidential primary...I have signed on with many others at Science Debate 2008 to urge the candidates to debate issues in science and technology, and would urge readers of this blog to do the same. Here are some comments by John Tierney.

Liberals are smarter than conservatives...?

A British study by Deary et al. titled "Bright Children become Enlightened Adults" (Psychological Science, Volume 19 pp. 1-6, January 2008) shows a correlation between general intelligence (g) at age 10 and liberal and anti-traditional social attitudes at age 30...

We examined the prospective association between general intelligence (g) at age 10 and liberal and antitraditional social attitudes at age 30 in a large (N = 7,070), representative sample of the British population born in 1970. Statistical analyses identified a general latent trait underlying attitudes that are antiracist, pro-working women, socially liberal, and trusting in the democratic political system. There was a strong association between higher g at age 10 and more liberal and antitraditional attitudes at age 30; this association was mediated partly via educational qualifications, but not at all via occupational social class. Very similar results were obtained for men and women. People in less professional occupations—and whose parents had been in less professional occupations—were less trusting of the democratic political system. This study confirms social attitudes as a major, novel field of adult human activity that is related to childhood intelligence differences.

Alarms and Anxiety in 2008 - guaranteed

John Tierney does a very nice piece in the Jan 1 NY Times Science section describing how activists, journalists and publicity-savvy scientists (called availability entrepreneurs by social scientists) selectively monitor the globe looking for newsworthy evidence of a new form of sinfulness, burning fossil fuels. Some clips from his text:

A year ago, British meteorologists made headlines predicting that the buildup of greenhouse gases would help make 2007 the hottest year on record. At year’s end, even though the British scientists reported the global temperature average was not a new record — it was actually lower than any year since 2001 — the BBC confidently proclaimed, “2007 Data Confirms Warming Trend.”

When the Arctic sea ice last year hit the lowest level ever recorded by satellites, it was big news and heralded as a sign that the whole planet was warming. When the Antarctic sea ice last year reached the highest level ever recorded by satellites, it was pretty much ignored. A large part of Antarctica has been cooling recently, but most coverage of that continent has focused on one small part that has warmed.

When Hurricane Katrina flooded New Orleans in 2005, it was supposed to be a harbinger of the stormier world predicted by some climate modelers. When the next two hurricane seasons were fairly calm — by some measures, last season in the Northern Hemisphere was the calmest in three decades — the availability entrepreneurs changed the subject. Droughts in California and Australia became the new harbingers of climate change (never mind that a warmer planet is projected to have more, not less, precipitation over all).

The most charitable excuse for this bias in weather divination is that the entrepreneurs are trying to offset another bias. The planet has indeed gotten warmer, and it is projected to keep warming because of greenhouse emissions, but this process is too slow to make much impact on the public.

When judging risks, we often go wrong by using what’s called the availability heuristic: we gauge a danger according to how many examples of it are readily available in our minds. Thus we overestimate the odds of dying in a terrorist attack or a plane crash because we’ve seen such dramatic deaths so often on television; we underestimate the risks of dying from a stroke because we don’t have so many vivid images readily available.

Slow warming doesn’t make for memorable images on television or in people’s minds, so activists, journalists and scientists have looked to hurricanes, wild fires and starving polar bears instead. They have used these images to start an “availability cascade,” a term coined by Timur Kuran, a professor of economics and law at the University of Southern California, and Cass R. Sunstein, a law professor at the University of Chicago.

The availability cascade is a self-perpetuating process: the more attention a danger gets, the more worried people become, leading to more news coverage and more fear. Once the images of Sept. 11 made terrorism seem a major threat, the press and the police lavished attention on potential new attacks and supposed plots. After Three Mile Island and “The China Syndrome,” minor malfunctions at nuclear power plants suddenly became newsworthy.

...Once a cascade is under way, it becomes tough to sort out risks because experts become reluctant to dispute the popular wisdom, and are ignored if they do. Now that the melting Arctic has become the symbol of global warming, there’s not much interest in hearing other explanations of why the ice is melting — or why the globe’s other pole isn’t melting, too.

Nature versus Nurture in Ventral Visual Cortex

Polk et al. do functional magnetic resonance imaging of monozygotic and dizygotic twins to show that genetics play a significant role in determining the cortical response to faces and places, more so than to orthographic stimuli (chairs or pseudowords). Here is their abstract, a paragraph from their concluding section and one figure from the paper.

Using functional magnetic resonance imaging, we estimated neural activity in twins to study genetic influences on the cortical response to categories of visual stimuli (faces, places, and pseudowords) that are known to elicit distinct patterns of activity in ventral visual cortex. The neural activity patterns in monozygotic twins were significantly more similar than in dizygotic twins for the face and place stimuli, but there was no effect of zygosity for pseudowords (or chairs, a control category). These results demonstrate that genetics play a significant role in determining the cortical response to faces and places, but play a significantly smaller role (if any) in the response to orthographic stimuli.


Figure legend: Patterns of estimated neural activity when viewing the four stimulus categories (axial slice). Functional activation maps were computed for the four contrasts of interest (faces, houses, pseudowords, and chairs relative to the phase-scrambled control condition), and the similarity measures (r) between these functional maps were computed for each twin pair. (Click on figure to enlarge)

The results of this study demonstrate that genetics play a significant role in determining the cortical response to faces and places. Of course, these findings do not imply that experience plays no role in determining the observed activity. To take just one example, genes that affect social behavior could potentially lead some people to look at faces and places more than other people, and the resulting difference in experience could lead to changes in the neural circuitry (we thank one of the anonymous reviewers for this example). The results simply demonstrate that genetics do play a crucial role. The results also show that genetics play a significantly smaller role in determining the cortical response to visually presented orthographic stimuli. Overall, the findings are consistent with the view that the cortical substrates of face recognition and place recognition are partially innately specified, but that the cortical response to orthographic stimuli is more dependent on experience. Face and place recognition are older than reading on an evolutionary scale, they are shared with other species, and they provide a clearer adaptive advantage. It is therefore plausible that evolution would shape the cortical response to faces and places, but not orthographic stimuli.