Moving and interacting with the environment require a reference for orientation and a scale for calibration in space and time. There is a wide variety of environmental clues and calibrated frames at different locales, but the reference of gravity is ubiquitous on Earth. The pull of gravity on static objects provides a plummet which, together with the horizontal plane, defines a three-dimensional Cartesian frame for visual images. On the other hand, the gravitational acceleration of falling objects can provide a time-stamp on events, because the motion duration of an object accelerated by gravity over a given path is fixed. Indeed, since ancient times, man has been using plumb bobs for spatial surveying, and water clocks or pendulum clocks for time keeping. Here we review behavioral evidence in favor of the hypothesis that the brain is endowed with mechanisms that exploit the presence of gravity to estimate the spatial orientation and the passage of time. Several visual and non-visual (vestibular, haptic, visceral) cues are merged to estimate the orientation of the visual vertical. However, the relative weight of each cue is not fixed, but depends on the specific task. Next, we show that an internal model of the effects of gravity is combined with multisensory signals to time the interception of falling objects, to time the passage through spatial landmarks during virtual navigation, to assess the duration of a gravitational motion, and to judge the naturalness of periodic motion under gravity.
BarlowH. B. (1959). Sensory mechanisms the reduction of redundancy and intelligence in: Proceedings of the National Physical Laboratory Symposium D. V. Blake and A. M. Uttley (Eds) pp. 537–559. H. M. Stationary Office London UK.
Vestibular perception is slow: a reviewMultisens. Res.26387–403.
Barnett-CowanM.MeilingerT.VidalM.TeufelH.BülthoffH. H. (2012).
MPI CyberMotion Simulator: implementation of a novel motion simulator to investigate multisensory path integration in three dimensionsJ. Vis. Exp.May10(63) e3436.
Contributions of the human temporoparietal junction and MT/V5+ to the timing of interception revealed by transcranial magnetic stimulationJ. Neurosci.2812071–12084.
BottiniG.KarnathH. O.VallarG.SterziR.FrithC. D.FrackowiakR. S. J.PaulesuE. (2001).
Cerebral representations for egocentric space. Functional-anatomical evidence from caloric vestibular stimulation and neck vibrationBrain1241182–1196.
De VrijerM.MedendorpW. P.Van GisbergenJ. A. M. (2008).
Shared computational mechanism for tilt compensation accounts for biased verticality percepts in motion and pattern visionJ. Neurophysiol.99915–930.
FernandezC.GoldbergJ. M. (1976).
Physiology of peripheral neurons innervating otolith organs of the squirrel monkey. I. Response to static tilts and to long-duration centrifugal forceJ. Neurophysiol.39970–984.
Anticipating the effects of visual gravity during simulated self-motion: estimates of time-to-passage along vertical and horizontal pathsExp. Brain Res.229579–586.
IndovinaI.MaffeiV.PauwelsK.MacalusoE.OrbanG. A.LacquanitiF. (2013b).
Simulated self-motion in a visual gravity field: sensitivity to vertical and horizontal heading in the human brainNeuroimage71114–124.
KlatzkyR. L. (1998).
Allocentric and egocentric spatial representations: definitions, distinctions, and interconnections in:
Spatial CognitionFreksaC.HabelC.WenderK. F. (Eds) pp.
1–17. SpringerBerlin/Heidelberg, Germany.
LacquanitiF.CarrozzoM.BorgheseN. A. (1993).
The role of vision in tuning anticipatory motor responses of the limbs in:
Multisensory Control of MovementBerthozA.GielenC.HennV.HoffmannK. P.ImbertM.LacquanitiF.RoucouxA. (Eds) pp.
379–393. Oxford University PressOxford, UK.
McIntyreJ.SenotP.PrevostP.ZagoM.LacquanitiF.BerthozA. (2003). The use of on-line perceptual invariants versus cognitive internal models for the predictive control of movement and action in: Proc. First Int. IEEE EMBS Conf. Neural Eng. Capri pp. 438–441.
MerchantH.HarringtonD. L.MeckW. H. (2013).
Neural basis of the perception and estimation of timeAnnu. Rev. Neurosci.36313–336.
ZagoM.BoscoG.MaffeiV.IosaM.IvanenkoY. P.LacquanitiF. (2005).
Fast adaptation of the internal model of gravity for manual interceptions: evidence for event-dependent learningJ. Neurophysiol.931055–1068.