The EEG correlates and dangerous behavioral consequences of drowsy driving after a single night of mild sleep deprivation.

OBJECTIVE: Here, we investigated the behavioral, cognitive, and electrophysiological impact of mild, acute sleep loss via simultaneously recorded behavioral and electrophysiological measures of vigilance during a "real-world", simulated driving task. METHODS: Participants (N = 34) visited the lab for two testing days where their brain activity and vigilance were simultaneously recorded during a driving simulator task. The driving task lasted approximately 70 mins and consisted of tailgating the lead car at high speed, which braked randomly, requiring participants to react quickly to avoid crashing. The night before testing, participants either slept from 12am-9am (Normally Rested), or 1am-6am (Sleep Restriction). RESULTS: After a single night of mild sleep restriction, sleepiness was increased, participants took longer to brake, missed more braking events, and crashed more often. Brain activity showed more intense alpha burst activity and significant changes in EEG spectral power frequencies related to arousal (e.g., delta, theta, alpha). Importantly, increases in amplitude and number of alpha bursts predicted delays in reaction time when braking. CONCLUSIONS: The findings of this study suggest that a single night of mild sleep loss has significant, negative consequences on driving performance and vigilance, and a clear impact on the physiology of the brain in ways that reflect reduced arousal. SIGNIFICANCE: Understanding neural and cognitive changes associated with sleep loss may lead to important advancements in identifying and preventing potentially dangerous sleep-related lapses in vigilance.

Age-related changes in amplitude, latency and specialization of ERP responses to faces and watches.

Healthy aging is associated with impairments in face recognition. While earlier research suggests that these impairments arise during memory retrieval, more recent findings suggest that earlier mechanisms, at the perceptual stage, may also be at play. However, results are often inconsistent and very few studies have included a non-face control stimulus to facilitate interpretation of results with respect to the implication of specialized face mechanisms vs. general cognitive factors. To address these issues, P100, N170 and P200 event-related potentials (ERPs) were measured during processing of faces and watches. For faces, age-related differences were found for P100, N170 and P200 ERPs. For watches, age-related differences were found for N170 and P200 ERPs. Older adults showed less selective and less lateralized N170 responses to faces, suggesting that ERPs can detect age-related de-differentiation of specialized face networks. We conclude that age-related impairments in face recognition arise in part from difficulties in the earliest perceptual stages of visual information processing. A working model is presented based on coarse-to-fine analysis of visually similar exemplars.

A comparative study of the performance of individuals with fragile X syndrome and Fmr1 knockout mice on Hebb-Williams mazes.

Fragile X syndrome (FXS) is the most prevalent form of heritable mental retardation. It arises from a mutation in the FMR1 gene on the X chromosome that interferes with expression of fragile X mental retardation protein (FMRP) and leads to a wide range of behavioural and cognitive deficits. Previous studies have shown a deficit in basic visual perceptual processing as well as spatial abilities in FXS. How such a deficit may impact spatial navigation remains unknown. The current study extended previous research by evaluating spatial learning and memory using both virtual and physical versions of Hebb-Williams mazes, which allows for testing of humans and animals under comparable conditions. We compared the performance of individuals affected by FXS to typically developing individuals of equivalent mental age as well as the performance of Fmr1 knockout mice to wild-type control mice on the same maze problems. In human participants, performance of the comparison group improved across trials, showing expected significant decreases in both errors and latency. In contrast, the performance of the fragile X group remained at similar levels across trials. Although wild-type control mice made significantly fewer errors than the Fmr1 knockout mice, latencies were not statistically different between the groups. These findings suggest that affected humans and mice show similar spatial learning deficits attributable to the lack of FMRP. The implications of these data are discussed including the notion that Hebb-Williams mazes may represent a useful tool to examine the impact of pharmacological interventions on mitigating or reversing the symptoms associated with FXS.

Does face recognition rely on encoding of 3-D surface? Examining the role of shape-from-shading and shape-from-stereo.

It is now well known that processing of shading information in face recognition is susceptible to bottom lighting and contrast reversal, an effect that may be due to a disruption of 3-D shape processing. The question then is whether the disruption can be rectified by other sources of 3-D information, such as shape-from-stereo. We examined this issue by comparing identification performance either with or without stereo information using top-lit and bottom-lit face stimuli in both photographic positive and negative conditions. The results show that none of the shading effects was reduced by the presence of stereo information. This finding supports the notion that shape-from-shading overrides shape-from-stereo in face perception. Although shape-from-stereo did produce some signs of facilitation for face identification, this effect was negligible. Together, our results support the view that 3-D shape processing plays only a minor role in face recognition. Our data are best accounted for by a weighted function of 2-D processing of shading pattern and 3-D processing of shapes, with a much greater weight assigned to 2-D pattern processing.

The effects of spatial frequency overlap on face recognition.

The effects of spatial frequency overlap between pairs of low-pass versus high-pass images on face recognition and matching were examined in 6 experiments. Overlap was defined as the range of spatial frequencies shared by a pair of filtered images. This factor was manipulated by processing image pairs with high-pass/low-pass filter pairs whose 50% cutoff points varied in their separation from one another. The effects of the center frequency of filter pairs were also investigated. In general, performance improved with greater overlap and higher center frequency. In control conditions, the image pairs were processed with identical filters and thus had complete overlap. Even severely filtered low-pass or high-pass images in these conditions produced superior performance. These results suggest that face recognition is more strongly affected by spatial frequency overlap than by the frequency content of the images.

Lighting direction affects recognition of untextured faces in photographic positive and negative.

Face recognition in photographic positive and negative was examined in a same/different matching task in five lighting direction conditions using untextured 3-D laser-scanned faces. The lighting directions were +60, +30, 0, -30 and -60 degrees, where negative values represent bottom lighting and positive values represent top lighting. Recognition performance was better for faces in positive than in negative when lighting directions were at +60 degrees. In one experiment, the same effect was also found at +30 degrees. However, faces in negative were recognized better than positive when the direction was -60 degrees. There was no difference in recognition performance when the lighting direction was 0 and -30 degrees. These results confirm that the effect of lighting direction can be a determinant of the photographic negative effect. Positive faces, which normally appear to be top-lit, may be difficult to recognize in negative partly because of the accompanying change in apparent lighting direction to bottom-lit.

A maximum motion technique for assessment of color vision defects.

Several luminance-matching methods, such as flicker fusion and the minimum motion technique (MMT), are capable of detecting certain forms of abnormal color vision. We present evidence that the heterochromatic fusion nystagmus (HFN) luminance matching technique can discriminate among normal trichromats, protanopes, and deuteranomals. The HFN luminance matching technique has the advantage that it provides a positive indication of isoluminance (maximization of motion) as opposed to the MMT and flicker fusion methods, which indicate isoluminance by the minimization of motion and flicker, respectively. We tested 16 normal trichromats, 6 protanopes, and 4 deuteranomals with the HFN technique. Results indicate that HFN is a useful tool for examining color vision. Because the HFN stimulus elicits reflexive eye movements (optokinetic nystagmus) that follow the apparent motion of the stimulus, HFN luminance matching will be particularly useful in animal and infant research, where other color vision tests are difficult to implement.