Browsing by Subject "DIRECTION"

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  • Lappi, Otto; Pekkanen, Jami; Rinkkala, Paavo; Tuhkanen, Samuel; Tuononen, Ari; Virtanen, Juho-Pekka (2020)
    It is well-established how visual stimuli and self-motion in laboratory conditions reliably elicit retinal-image-stabilizing compensatory eye movements (CEM). Their organization and roles in natural-task gaze strategies is much less understood: are CEM applied in active sampling of visual information in human locomotion in the wild? If so, how? And what are the implications for guidance? Here, we directly compare gaze behavior in the real world (driving a car) and a fixed base simulation steering task. A strong and quantifiable correspondence between self-rotation and CEM counter-rotation is found across a range of speeds. This gaze behavior is “optokinetic”, i.e. optic flow is a sufficient stimulus to spontaneously elicit it in naïve subjects and vestibular stimulation or stereopsis are not critical. Theoretically, the observed nystagmus behavior is consistent with tracking waypoints on the future path, and predicted by waypoint models of locomotor control - but inconsistent with travel point models, such as the popular tangent point model.
  • Vainio, Lari; Tiainen, Mikko (2018)
    Past studies have revealed connections in directional programming between hands. The present study investigated whether there could also be interaction in programming proximal and distal components of a prehensile hand action. In Experiment 1, the participants performed simultaneously either a push or pull response with the left hand and the grip closure or opening with the right hand. In Experiment 2, the push and pull responses of the left hand were performed together with the precision or power grip responses of the right hand. The participants showed preference, measured in reaction times, to couple the push response with the grip opening and the precision grip, whereas the pull response was associated with the grip closure and the power grip. The study shows for the first time a systematic interaction in proximal and distal prehensile components between two hands. We propose that these effects reflect inter- and intra-limb connections between the representations that prepare the arm extension for the outward reaching, the finger extension for the grip opening, and the motor processes that prepare the precision grip. Conversely, there appear to be connections between the representations that prepare the arm flexion for the inward directed hand movements, the flexion of the thumb and the fingers for the grip closure, and flexion of four fingers for the power grip.
  • Vainio, Lari; Tiippana, Kaisa; Tiainen, Mikko; Rantala, Aleksi; Vainio, Martti (2018)
    Research has shown connections between articulatory mouth actions and manual actions. This study investigates whether forward-backward hand movements could be associated with vowel production processes that programme tongue fronting/backing, lip rounding/spreading (Experiment 1), and/or consonant production processes that programme tongue tip and tongue dorsum actions (Experiment 2). The participants had to perform either forward or backward hand movement and simultaneously pronounce different vowels or consonants. The results revealed a response benefit, measured in vocal and manual reaction times, when the responses consisted of front vowels and forward hand movements. Conversely, back vowels were associated with backward hand movements. Articulation of rounded versus unrounded vowels or coronal versus dorsal consonants did not produce the effect. In contrast, when the manual responses of forward-backward hand movements were replaced by precision and power grip responses, the coronal consonants [t] and [r] were associated with the precision grip, whereas the dorsal consonant [k] was associated with the power grip. We propose that the movements of the tongue body, operating mainly for vowel production, share the directional action planning processes with the hand movements. Conversely, the tongue articulators related to tongue tip and dorsum movements, operating mainly for consonant production, share the action planning processes with the precision and power grip, respectively.
  • Vainio, Lari; Tiippana, Kaisa; Tiainen, Mikko; Rantala, Aleksi; Vainio, Martti (2018)
    Research has shown connections between articulatory mouth actions and manual actions. This study investigates whether forward-backward hand movements could be associated with vowel production processes that programme tongue fronting/backing, lip rounding/spreading (Experiment 1), and/or consonant production processes that programme tongue tip and tongue dorsum actions (Experiment 2). The participants had to perform either forward or backward hand movement and simultaneously pronounce different vowels or consonants. The results revealed a response benefit, measured in vocal and manual reaction times, when the responses consisted of front vowels and forward hand movements. Conversely, back vowels were associated with backward hand movements. Articulation of rounded versus unrounded vowels or coronal versus dorsal consonants did not produce the effect. In contrast, when the manual responses of forward-backward hand movements were replaced by precision and power grip responses, the coronal consonants [t] and [r] were associated with the precision grip, whereas the dorsal consonant [k] was associated with the power grip. We propose that the movements of the tongue body, operating mainly for vowel production, share the directional action planning processes with the hand movements. Conversely, the tongue articulators related to tongue tip and dorsum movements, operating mainly for consonant production, share the action planning processes with the precision and power grip, respectively.
  • Kilpelainen, Markku; Putnam, Nicole M.; Ratnam, Kavitha; Roorda, Austin (2021)
    Due to the dramatic difference in spatial resolution between the central fovea and the surrounding retinal regions, accurate fixation on important objects is critical for humans. It is known that the preferred retinal location (PRL) for fixation of healthy human observers rarely coincides with the retinal location with the highest cone density. It is not currently known, however, whether the PRL is consistent within an observer or is subject to fluctuations and, moreover, whether observers' subjective fixation location coincides with the PRL. We studied whether the PRL changes between days. We used an adaptive optics scanning laser ophthalmoscope to project a Maltese cross fixation target on an observer's retina and continuously imaged the exact retinal location of the target. We found that observers consistently use the same PRL across days, regardless of how much the PRL is displaced from the cone density peak location. We then showed observers small stimuli near the visual field location on which they fixated, and the observers judged whether or not the stimuli appeared in fixation. Observers' precision in this task approached that of fixation itself. Observers based their judgment on both the visual scene coordinates and the retinal location of the stimuli. We conclude that the PRL in a normally functioning visual system is fixed, and observers use it as a reference point in judging stimulus locations.