The effects of pattern shape, subliminal stimulation, and voluntary control on multistable visual perception.

Spontaneous figure reversal of ambiguous patterns was analyzed in humans. A) With Necker-"cube"-like, or "drum"-like figures, having square or round shaped "front" and "rear" surfaces, and either large or small "depth", the perceptual intervals corresponding to both interpretations of "drum" were longer than those of "cube"; the perceived "depth" of the figures was less relevant for reversal timing (inter-reversal intervals were only slightly longer for the "deeper" figures). Although the shape of "front" and "rear" surfaces is not a crucial geometrical feature for figure reversal, it did influence its timing.

First identification and localization of a visual pigment in Hydra (Cnidaria, Hydrozoa).

The cnidarian Hydra does not possess identified photoreceptive structures or specialized cells for light detection; nevertheless, it shows a marked photosensitivity. So far no evidence has been previously reported about the localization of the proteins involved in the photoresponse. We used polyclonal antibodies and immunofluorescence microscopy on whole-mount Hydra to identify a putative rhodopsin-like protein.

Photobehaviour of Hydra (Cnidaria, Hydrozoa) and correlated mechanisms: a case of extraocular photosensitivity.

The morpho-functional organization correlated to photosensitivity in Cnidaria is that of ocelli and extraocular photoreception. Several examples of the second type of organization are reported. The photosensitivity of the cnidarian Hydra is of the extraocular (neural or dermal) type.

EXPLAN--a programming language for complex visual stimuli presentation.

Visual cognition research requires the flexible use of structured spatial patterns, characterized by various space and time parameters, which may be administered as visual stimuli. Dealing with this kind of study, we developed a special-purpose programming language and implemented a compiler to build executable programs. The language allows the presentation of stimuli, their space coordinates, persistency values, sequence, kinematic parameters, space-time proximity with other visual stimuli, determination of their modification according to external interaction, generation of subliminal stimuli, monitoring of different subject reactions, automatic reporting of stimulus presentation, and reaction monitoring.

Modulation of membrane potential in algal cells by temperature gradients. A thermodynamic approach.

The aim of the present study is to ascertain whether transmembrane temperature gradients couple with transport of electric charge in living cells of Valonia utricularis and eventually measure the thermodynamic coupling coefficient (s). Simple experimental procedures are described that allow generation of temperature gradients of predetermined sense and intensity across the cell membrane. Simultaneous measurement of the potential difference is ensured by standard electrophysiological methods.