A progressively wetter climate in southern East Africa over the past 1.3 million years.

African climate is generally considered to have evolved towards progressively drier conditions over the past few million years, with increased variability as glacial-interglacial change intensified worldwide. Palaeoclimate records derived mainly from northern Africa exhibit a 100,000-year (eccentricity) cycle overprinted on a pronounced 20,000-year (precession) beat, driven by orbital forcing of summer insolation, global ice volume and long-lived atmospheric greenhouse gases. Here we present a 1.3-million-year-long climate history from the Lake Malawi basin (10°-14° S in eastern Africa), which displays strong 100,000-year (eccentricity) cycles of temperature and rainfall following the Mid-Pleistocene Transition around 900,000 years ago. Interglacial periods were relatively warm and moist, while ice ages were cool and dry. The Malawi record shows limited evidence for precessional variability, which we attribute to the opposing effects of austral summer insolation and the temporal/spatial pattern of sea surface temperature in the Indian Ocean. The temperature history of the Malawi basin, at least for the past 500,000 years, strongly resembles past changes in atmospheric carbon dioxide and terrigenous dust flux in the tropical Pacific Ocean, but not in global ice volume. Climate in this sector of eastern Africa (unlike northern Africa) evolved from a predominantly arid environment with high-frequency variability to generally wetter conditions with more prolonged wet and dry intervals.

Response to Comment on "Atlantic and Pacific multidecadal oscillations and Northern Hemisphere temperatures".

Kravtsov et al. claim that we incorrectly assess the statistical independence of simulated samples of internal climate variability and that we underestimate uncertainty in our calculations of observed internal variability. Their analysis is fundamentally flawed, owing to the use of model ensembles with too few realizations and the fact that no one model can adequately represent the forced signal.

Biological risk of older adults with visual impairments.

OBJECTIVES: To investigate whether biological markers of health differ among older adults with visual impairment compared to those with normal vision. DESIGN: We use data from the National Health and Nutrition Examination Survey (1999 - 2006) to investigate clinically defined at-risk levels for 10 biological markers. SETTING: Survey participants were non-institutionalized. PARTICIPANTS: Nationally representative (U.S.) sample of older adults age 65 and older, categorized as having blindness (20/200 or worse), low vision (20/40 to 20/100) or normal vision (better than 20/40). INTERVENTION: Separate binary logistic regressions (one for each biomarker, with two at-risk cut points for BMI: obese and underweight) were computed to determine the odds of having at-risk levels of each biomarker. MEASUREMENTS: Biomarkers included: systolic and diastolic blood pressure, high-density lipoprotein, low-density lipoprotein (LDL) cholesterol, total cholesterol, glycated hemoglobin, body mass index (BMI), fasting triglycerides, C-reactive protein, and plasma homocysteine. RESULTS: Older adults who were blind were more likely to have high-risk levels of LDL cholesterol, homocysteine, and to be underweight (BMI>18.5). Similarly, older adults with LV were more likely to have high-risk levels of homocysteine compared to older adults with normal vision. CONCLUSION: As several of the high-risk biomarkers associated with visual impairment were diet-related, our results suggest the importance of nutrition and diet programs aimed towards educating older people who are visually impaired.

Vision and attention. II: Is visual attention a mechanism through which a deficient magnocellular pathway might cause reading disability?

Recent research in reading disability has discovered that at least some reading-disabled subjects have deficits in their magnocellular (M) visual pathways. However, the mechanism by which M pathway deficits affect reading has not been addressed. Abnormal attention has long been known to be associated with reading-disabled individuals, and new research in visual attention has determined that transient visual attention is dominated by M-stream inputs. The purpose of this study was to determine whether visual attention might be the mechanism through which a faulty M pathway could produce visual deficits in reading-disabled subjects. Spatiotemporal attentional response functions were measured using the Line Motion Illusion and compared in normal and disabled readers. Specific abnormalities in the visual attention mechanisms of disabled readers were found which might suggest mechanisms by which reading could be affected by a deficient M stream.

Vision and attention. I: Current models of visual attention.

Visual attention has been defined by different researchers and clinicians in a variety of ways that are sometimes conflicting or confusing. This paper will provide a unified definition of visual attention, as well as a putative neurophysiological mechanism that is consistent with this unified definition. In addition, recent data on the mechanisms of visual attention will be presented, including its spatial organization and temporal dependencies, as well as the role of parallel visual pathways in its activation.

Transient visual attention is dominated by the magnocellular stream.

Robust visual attentional responses are produced by the sudden onset of a visual cue, but the properties of cues that best elicit an attentional response are not fully known. We used the line-motion illusion (Hikosaka et al., 1991) to investigate the optimal cue properties that evoke visual attention. We found that visual attention is driven primarily by the luminance contrast of the cue. Furthermore, by manipulating the spatial, chromatic, and contrast properties of cues, we found that magnocellular (M) stream biased cues always override the response to parvocellular (P) stream biased cues, even when the P stream biased cues are presented first. Our data suggest that cues that preferentially excite the M pathway predominantly capture visual attention.

Visual attention mechanisms show a center-surround organization.

The sudden onset of a cue triggers visual attention, which then enhances visual processing in the zone near the cue. This enhancement causes a motion illusion in subsequent stimuli presented near the cue. At greater separations from the cue, the illusory motion reverses direction, indicating prolonged processing speed. Measurements of the strength and direction of illusory motion at increasing separations from the cue reveal an attentional 'perceptive field' with an excitatory center at the locus cued and an inhibitory surround subtending the remaining visual field. These findings help explain the traditional attentional 'benefits' and 'costs' of attention.

A sensory explanation for visual attention deficits in the elderly.

BACKGROUND: Reduced visual attention has been implicated as a major factor in age-related deficits of real-world functioning such as driving. However, the contribution of sensory factors to visual attention deficits has not been delineated. The magnocellular stream, which is diminished in aging, provides the dominant input to attention, and could provide a direct visual sensory explanation for these attentional losses. METHODS: We measured temporal response curves for transient visual attention in older and younger subjects. Attentional cues stimulated both the magnocellular and parvocellular streams. RESULTS: Older subjects exhibited slower, weaker responses than younger subjects. The time course in younger subjects agreed with that obtained for magnocellular(M)-biased stimuli, whereas that of older subjects agreed with parvocellular(P)-biased responses. CONCLUSIONS: The activation of transient visual attention is slower and weaker for elderly subjects, reflecting a reduced magnocellular input. This marks a primary visual cause for visual attention deficits of the elderly.

Monocular accommodative fluctuations associated with temporomandibular joint syndrome.

A young scientist reported severe headaches emanating from behind one eye with an associated intermittent monocular blur. The monocular near cross-cylinder test revealed an accommodative fluctuation of one eye alone with a range of approximately 3 D. Referral to a neuro-ophthalmologist failed to produce a diagnosis for the disorder. A subsequent routine visit to a dentist provided a diagnosis of Costen's temporomandibular joint (TMJ) syndrome, a condition that is commonly misdiagnosed as a variety of neurological and vascular disorders.