ABSTRACT
The earliest human graphic productions, consisting of abstract patterns engraved on a variety of media, date to the Lower and Middle Palaeolithic. They are associated with anatomically modern and archaic hominins. The nature and significance of these engravings are still under question. To address this issue, we used functional magnetic resonance imaging to compare brain activations triggered by the perception of engraved patterns dating between 540 000 and 30 000 years before the present with those elicited by the perception of scenes, objects, symbol-like characters and written words. The perception of the engravings bilaterally activated regions along the ventral route in a pattern similar to that activated by the perception of objects, suggesting that these graphic productions are processed as organized visual representations in the brain. Moreover, the perception of the engravings led to a leftward activation of the visual word form area. These results support the hypothesis that these engravings have the visual properties of meaningful representations in present-day humans, and could have served such purpose in early modern humans and archaic hominins.
ABSTRACT
We report on the second harmonic generation of deep UV light in beta -BaB(2)O(4) (BBO) waveguides pumped by a frequency-doubled continuous-wave Nd:YAG laser. An output power of 0.32 mW at 266 nm has been achieved for an internal pump power of 670 mW. Optical channel waveguides in BBO crystals were produced by He(+) ion implantation, lithographic masking and ion etching. The linear and nonlinear optical properties and the power handling capability of these waveguides are presented.
