Seeing faces: evidence suggesting cortical disinhibition in the genesis of visual hallucinations.

The neural mechanisms responsible for triggering visual hallucinations are poorly understood. Here, we report a unique patient whose hallucinations consist exclusively of faces, and which could be reliably precipitated by looking at trees. Using functional Magnetic Resonance Imaging (fMRI), we found that, while face hallucinations was associated with increased neural activity in a number of cortical regions, including low-level visual areas, there was significant decreased activity in the right fusiform face area, a region that is empirically defined by increase activity during veridical perception of faces. These findings indicate key differences in how hallucinatory and veridical perceptions lead to the same phenomenological experience of seeing faces, and are consistent with the hypothesis that hallucinations may be generated by decreased inhibitory inputs to key cortical regions, in contrast to the excitatory synaptic inputs underlying veridical perception

Conversion from Staple to Cash Crop Production in Mexico After NAFTA: Effects of PROCAMPO and Credit Constraints

In this paper, we ask whether PROCAMPO helped Mexican agricultural producers benefit from NAFTA. Specifically, we explore the effect of these decoupled income payments (PROCAMPO) on producers’ ability to switch to cash crop production, and whether these payments help alleviate credit constraints for poorer producers. Given that WTO negotiations are currently stalled in part because of the trade concerns of developing nations, exploring the constraints that small producers face and whether decoupled subsidies can assist those producers in benefiting from new markets is important. Unlike previous studies, who concentrated on specific regions and ejidal lands, we use nationwide county-level data, which allows for us to see the regional distribution of change across Mexico. We use these data to estimate the change in staple crop production as a function of county-level characteristics. We find some evidence to support the hypothesis that an increase in PROCAMPO payments leads to a decrease in the area planted in staples. Second, the implementation of NAFTA is associated with greater cash crop production and we can see that the creation of new markets is, in general, leading to a reduction in land planted in staples. Third, we find that the effect of PROCAMPO is even larger for ejido producers, implying that their benefits are not constrained to larger producers. Last, we find evidence that areas closest to the United States border have seen a greater movement to cash crop production after NAFTA.NAFTA, PROCAMPO, Credit Constraint, Mexico, staple production, crop choice, International Relations/Trade,

Multiplexed DNA-Modified Electrodes

We report the use of silicon chips with 16 DNA-modified electrodes (DME chips) utilizing DNA-mediated charge transport for multiplexed detection of DNA and DNA-binding protein targets. Four DNA sequences were simultaneously distinguished on a single DME chip with 4-fold redundancy, including one incorporating a single base mismatch. These chips also enabled investigation of the sequence-specific activity of the restriction enzyme Alu1. DME chips supported dense DNA monolayer formation with high reproducibility, as confirmed by statistical comparison to commercially available rod electrodes. The working electrode areas on the chips were reduced to 10 μm in diameter, revealing microelectrode behavior that is beneficial for high sensitivity and rapid kinetic analysis. These results illustrate how DME chips facilitate sensitive and selective detection of DNA and DNA-binding protein targets in a robust and internally standardized multiplexed format

Competitiveness of Brazilian Sugarcane Ethanol Compared to US Corn Ethanol

Corn ethanol produced in the US and sugarcane ethanol produced in Brazil are the world’s leading sources of biofuel. Current US biofuel policies create both incentives and constraints for the import of ethanol from Brazil, and together with the competitiveness and greenhouse gas intensity of sugarcane ethanol compared to corn ethanol will determine the extent of these imports. This study analyzes the supply-side determinants of this competitiveness and compares the greenhouse gas intensity of corn ethanol and sugarcane ethanol delivered to US ports. We find that while the cost of sugarcane ethanol production in Brazil is lower than that of corn ethanol in the US, the inclusion of transportation costs for the former and co-product credits for the latter changes their relative competitiveness. We also find that the relative cost of ethanol in the US and Brazil is highly sensitive to the prevailing exchange rate and prices of feedstocks. At an exchange rate of US$1 = R$2.15 the cost of corn ethanol is 15% lower than the delivered cost of sugarcane ethanol at a US port. Sugarcane ethanol has lower GHG emissions than corn ethanol but a price of over $113 per ton of CO2 is needed to affect competitiveness.economic competitiveness, renewable fuel standard, ethanol trade policy, Agribusiness, Agricultural and Food Policy,

A Vertical Asymmetry in Saccades

Visual exploration of natural scenes imposes demands that differ between the upper and the lower visual hemifield. Yet little is known about how ocular motor performance is affected by the location of visual stimuli or the direction of a behavioural response. We compared saccadic latencies between upper and lower hemifield in a variety of conditions, including short-latency prosaccades, long-latency prosaccades, antisaccades, memory-guided saccades and saccades with increased attentional and selection demand. All saccade types, except memory guided saccades, had shorter latencies when saccades were directed towards the upper field as compared to downward saccades (

The inter-trial spatial biases of stimuli and goals in saccadic programming

Prior studies have shown an ‘alternate antisaccade-goal bias’, in that the saccadic landing points of antisaccades were displaced towards the location of antisaccade goals used in other trials in the same experimental block. Thus the motor response in one trial induced a spatial bias of a motor response in another trial. In this study we investigated whether sensory information, i.e. the location of a visual stimulus, might have a spatial effect on a motor response too. Such an effect might be attractive as for the alternate antisaccade-goal bias or repulsive. For this purpose we used block of trials with either antisaccades, prosaccades or mixed trials in order to study the alternate-trial biases generated by antisaccade goals, antisaccade stimuli, and prosaccade goals. in contrast to the effects of alternate antisaccade goals described in prior studies, alternate antisaccade stimuli generated a significant repulsive bias of about 1.8°: furthermore, if stimulus and motor goal coincide, as with an alternate prosaccade, the repulsive effect of a stimulus prevails, causing a bias of about 0.9°. Taken together with prior results, these findings may reflect averaging of current and alternate trial activity in a salience map, with excitatory activity from the motor response and inhibitory activity from the sensory input.

Trial history biases the spatial programming of antisaccades

The historical context in which saccades are made influences their latency and error rates, but less is known about how context influences their spatial parameters. We recently described a novel spatial bias for antisaccades, in which the endpoints of these responses deviate towards alternative goal locations used in the same experimental block, and showed that expectancy (prior probability) is at least partly responsible for this ‘alternate-goal bias'. In this report we asked whether trial history also plays a role. Subjects performed antisaccades to a stimulus randomly located on the horizontal meridian, on a 40° angle downwards from the horizontal meridian, or on a 40° upward angle, with all three locations equally probable on any given trial. We found that the endpoints of antisaccades were significantly displaced towards the goal location of not only the immediately preceding trial (n−1) but also the penultimate (n−2) trial. Furthermore, this bias was mainly present for antisaccades with a short latency of <250ms and was rapidly corrected by secondary saccades. We conclude that the location of recent antisaccades biases the spatial programming of upcoming antisaccades, that this historical effect persists over many seconds, and that it influences mainly rapidly generated eye movements. Because corrective saccades eliminate the historical bias, we suggest that the bias arises in processes generating the response vector, rather than processes generating the perceptual estimate of goal locatio

Systematic diagonal and vertical errors in antisaccades and memory-guided saccades

Studies of memory-guided saccades in monkeys show an upward bias, while studies of antisaccades in humans show a diagonal effect, a deviation of endpoints toward the 45° diagonal. To determine if these two different spatial biases are specific to different types of saccades, we studied prosaccades, antisaccades and memory-guided saccades in humans. The diagonal effect occurred not with prosaccades but with antisaccades and memory-guided saccades with long intervals, consistent with hypotheses that it originates in computations of goal location under conditions of uncertainty. There was a small upward bias for memory-guided saccades but not prosaccades or antisaccades. Thus this bias is not a general effect of target uncertainty but a property specific to memory-guided saccades

Cross-orientation transfer of adaptation for facial identity is asymmetric: A study using contrast-based recognition thresholds

AbstractRecent studies suggest that adaptation effects for face shape and gender transfer from upright to inverted faces more than the reverse. We investigated whether a similar asymmetry occurred for face identity, using a recently developed adaptation method based on contrast-recognition thresholds. When adapting and test stimuli shared the same orientation, aftereffects were similar for upright and inverted faces. When orientation differed, there was significant transfer of aftereffects from upright adapting to inverted test faces, but none from inverted to upright faces. We show that asymmetric cross-orientation transfer of face aftereffects generalize across two distinct face adaptation paradigms: the previously used perceptual-bias methodology and the recently introduced contrast-threshold based adaptation paradigm. These results also represent a generalization from aftereffects for face shape and gender to aftereffects for face identity. While these results are consistent with the dual-mode hypothesis, they can also be accounted for by a single population of units of varying orientation selectivity