Interocular Transfer Of Adaptation Research Articles

Monocular and binocular mechanisms mediating flicker adaptation

Flicker adaptation reduces subsequent temporal contrast sensitivity. Recent studies show that this adaptation likely results from neural changes in the magnocellular visual pathway, but whether this adaptation occurs at a monocular or a binocular level, or both, is unclear. Here, two experiments address this question. The first experiment exploits the observation that flicker adaptation is stronger at higher than lower temporal frequencies. Observers' two eyes adapted to 3Hz flicker with an incremental pulse at 1/4 duty cycle, either in-phase or out-of-phase in the two eyes. At the binocular level, the flicker rate was 6Hz in the out-of-phase condition if the two eyes' pulse trains sum. Similar sensitivity reduction was found in both phase conditions, as expected for independent monocular adapting mechanisms. The second experiment tested for interocular transfer of adaptation between eyes. Results showed that (1) flicker adaptation was strongest with adapting and test fields in only the same eye, (2) adaptation can be partially transferred interocularly with adaptation in only the opposite eye, and (3) adaptation was weakened when both eyes were adapted simultaneously at different contrasts, compared to test-eye adaptation alone. Taken together, the findings are consistent with mechanisms of flicker adaptation at both the monocular and binocular level.

Interocular transfer of orientation-specific fMRI adaptation reveals amblyopia-related deficits in humans

We devised an experimental strategy for assessing the cortical cross-talk between ocular subsystems. For this purpose we measured the interocular transfer of adaptation (IOTA) at different levels in the human brain, using orientation-selective fMRI adaptation. We tested 10 normally sighted and 10 stereoblind or stereodeficient amblyopic observers by adapting monocularly to phase-reversing, oblique sinusoidal gratings. Following monocular adaptation, cortical activations evoked by the same ( monoptic) or the other eye ( interocular) were measured for the same and for the orthogonal orientation in a two by two factorial design. In both experimental groups, we obtained significant orientation-selective monocular adaptation in area V1 and in extrastriate regions on the dorsal and ventral visual pathways. In the normally-sighted subjects we found in addition interocular adaptation in V1 and extrastriate visual areas. This interocular adaptation indicates that fMRI adaptation transfers from the adapted ocular subsystem to the non-adapted ocular subsystem, and thus provides a measure of binocular interaction in normally-sighted subjects. In the amblyopic subjects, no interocular adaptation was seen at any of the investigated cortical levels, regardless of which eye was adapted. We suggest that the abnormal pattern of interocular transfer of fMRI adaptation is related to the disturbed integration of binocular signals in amblyopia.

Interocular Transfer of Adaptation in the Primary Visual Cortex

Prolonged viewing of an unchanging pattern causes adaptation, which can be demonstrated by visual aftereffects such as the tilt and waterfall illusions. In normal observers, these typically exhibit interocular transfer (IOT), being observed when the adapting and test stimuli are shown to different eyes. Convergence of inputs from both eyes upon binocular neurons only occurs in the primary visual cortex (V1), and adaptation is substantially a cortical phenomenon. However, little is known about a physiological substrate of IOT in V1 and how it relates to the binocularity of neurons and local ocular dominance (OD) column architecture. We employed optical imaging to obtain OD maps in cat V1 and recorded from single neurons at targeted penetration sites to quantify their adaptation by drifting gratings when adapter and test stimulus were presented either to the same or to the opposite eyes. In contrast to earlier reports, clear IOT of adaptation was observed for binocular as well as monocular neurons; at population level, its strength amounted to 55%. Moreover, the position of the cells with respect to OD column borders had no significant effect on the strength of IOT. IOT does not appear to strongly depend on conventional binocularity of neurons.

A Pilot Study for Investigating Cortical Binocularity in Humans using fMRI Adaptation

Disrupted stereovision is a feature that accompanies strabismus. This study uses an fMRI adaptation paradigm to assess the amount of cortical binocularity in subjects with normal or impaired stereopsis. We present data from a pilot study of two normally-sighted and one stereodeficient subject with alternating fixation. We adapted one eye to diagonally oriented sinusoidal gratings and tested either the same (monocular test) or the other eye (interocular transfer), using either the same or an orthogonal orientation. In normally-sighted subjects, we observed monocular adaptation but only weak interocular transfer in the striate cortex, whereas in the extrastriate cortex we found strong monocular as well as interocular adaptation. In the stereodeficient subject, monocular adaptation but no interocular transfer was obtained in the extrastriate cortex. These results suggest that impaired stereopsis is related to reduced interocular transfer of adaptation at higher levels of the cortical visual pathway.

Stereodeficient subjects show substantial differences in interocular transfer of two motion adaptation aftereffects.

Interocular transfer (IOT) of two motion aftereffects was examined in subjects with normal and deficient stereopsis. Normal subjects showed complete (100%) IOT of motion adaptation on coherent motion thresholds, but only partial IOT of a conventional motion aftereffect, supporting suggestions that the latter aftereffect may be mediated at a lower level in the visual pathway than the extrastriate regions implicated in processing coherent motion. This idea was strengthened by an even greater dissociation between the extent of IOT of the two aftereffects among stereodeficient subjects who exhibited very low IOT of the conventional motion aftereffect, but high (> 87%) IOT of the coherence motion aftereffect.

Oculomotor adaptation to prisms: complete transfer between eyes.

It is argued that previous experiments investigating interocular transfer of adaptation have been concerned with an adaptation of the registered position of the limb used to indicate direction. Thus the question of interocular transfer of adaptation sited at the eye remains open. Two experiments are reported. The first showed that there was complete transfer between exposed and unexposed eyes. The conditions were such that the adaptation could be explained only as a change in the registered position of the eye in the head, or of the head on the shoulders. The second experiment showed that changes of this latter kind did not occur.

On the relation between interocular transfer of adaptation and Hering's law of equal innervation.

On the relation between interocular transfer of adaptation and Hering's law of equal innervation.