Visual imagination and cognitive mapping of a virtual building.

We investigated the contribution of visual imagination to the cognitive mapping of a building when initial exploration was simulated either visually by using a passive video walk-through, or mentally by using verbal guidance. Building layout had repeating elements with either rotational or mirror symmetry. Cognitive mapping of the virtual building, determined using questionnaires and map drawings, was present following verbal guidance but inferior to that following video guidance. Mapping was not affected by the building's structural symmetry. However, notably, it correlated with small-scale mental rotation scores for both video and verbal guidance conditions. There was no difference between males and females. A common factor that may have influenced cognitive mapping was the availability of visual information about the relationships of the building elements, either directly perceived (during the video walk-through) or imagined (during the verbal walk-through and/or during recall). Differences in visual imagination, particularly mental rotation, may thus account for some of the individual variance in cognitive mapping of complex built environments, which is relevant to how designers provide navigation-relevant information.

Hearing through Your Eyes: Neural Basis of Audiovisual Cross-activation, Revealed by Transcranial Alternating Current Stimulation.

Some people experience auditory sensations when seeing visual flashes or movements. This prevalent synaesthesia-like visually evoked auditory response (vEAR) could result either from overexuberant cross-activation between brain areas and/or reduced inhibition of normally occurring cross-activation. We have used transcranial alternating current stimulation (tACS) to test these theories. We applied tACS at 10 Hz (alpha band frequency) or 40 Hz (gamma band), bilaterally either to temporal or occipital sites, while measuring same/different discrimination of paired auditory (A) versus visual (V) Morse code sequences. At debriefing, participants were classified as vEAR or non-vEAR, depending on whether they reported "hearing" the silent flashes. In non-vEAR participants, temporal 10-Hz tACS caused impairment of A performance, which correlated with improved V; conversely under occipital tACS, poorer V performance correlated with improved A. This reciprocal pattern suggests that sensory cortices are normally mutually inhibitory and that alpha-frequency tACS may bias the balance of competition between them. vEAR participants showed no tACS effects, consistent with reduced inhibition, or enhanced cooperation between modalities. In addition, temporal 40-Hz tACS impaired V performance, specifically in individuals who showed a performance advantage for V (relative to A). Gamma-frequency tACS may therefore modulate the ability of these individuals to benefit from recoding flashes into the auditory modality, possibly by disrupting cross-activation of auditory areas by visual stimulation. Our results support both theories, suggesting that vEAR may depend on disinhibition of normally occurring sensory cross-activation, which may be expressed more strongly in some individuals. Furthermore, endogenous alpha- and gamma-frequency oscillations may function respectively to inhibit or promote this cross-activation.

Applications in sleep: How light affects sleep.

Sleep is an active physiological state that plays a critical role in our physical and mental health and well-being. It is generated by a complex interplay between two oscillators, namely, the circadian oscillator and the sleep-wake homeostat. Sleep propensity is a function of wakefulness, that is, the longer one is awake the greater the homeostatic sleep pressure. Sleep onset occurs as a wake promoting circadian signal subsides, coinciding with an evening rise in melatonin and drop in core temperature. Light is one of the strongest time signals for the circadian oscillator. Poor sleep is a prevalent complaint today, attributable, in part, to our easy access to artificial light, especially after dusk. This non-visual effect of light is mediated by a multi-component photoreceptive system, consisting of rods, cones and melanopsin-expressing intrinsically-photosensitive retinal ganglion cells (ipRGC). Perhaps, with this available biological knowledge we can engineer artificial light to minimize its disruptive effect on sleep. We will highlight this by discussing circadian photoreception and its effect on sleep, in the blind population.

Weighted integration suggests that visual and tactile signals provide independent estimates about duration.

Humans might possess either a single (amodal) internal clock or multiple clocks for different sensory modalities. Sensitivity could be improved by the provision of multiple signals. Such improvements can be predicted quantitatively, assuming estimates are combined by summation, a process described as optimal when summation is weighted in accordance with the variance associated with each of the initially independent estimates. This possibility was assessed for visual and tactile information regarding temporal intervals. In Experiment 1, 12 musicians and 12 nonmusicians judged durations of 300 and 600 ms, compared to test values spanning these standards. Bimodal precision increased relative to unimodal conditions, but not to the extent predicted by optimally weighted summation. In Experiment 2, 6 musicians and 6 other participants each judged 6 standards, ranging from 100 ms to 600 ms, with conflicting cues providing a measure of the weight assigned to each sensory modality. A weighted integration model best fitted these data, with musicians more likely to select near-optimal weights than nonmusicians. Overall, data were consistent with the existence of separate visual and tactile clock components at either the counter/integrator or memory stages. Independent estimates are passed to a decisional process, but not always combined in a statistically optimal fashion. (PsycINFO Database Record