# Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Zink et al. (1998)

#### 2.2. Linear Models

_{ocular}is ocular torsion in degrees, V is vestibular input in mA, a

_{o}is the slope in degrees per mA, and b

_{o}the intercept in degrees in the relationship between ocular torsion and visual tilt. T

_{visual}is visual tilt in degrees, a

_{v}is the slope in degrees per mA, and b

_{v}is the intercept in degrees.

#### 2.3. Directly Proportional Linear Models

_{o}parameter in Equation (1) means that the eye is in two different orientations at the same time when no stimulation is applied. The same is true for the a

_{v}parameter in Equation (2): non-zero values would mean visual perception will be tilted in two directions at the same time when no stimulation is applied.

_{ocular}is ocular torsion in degrees, V is vestibular input in mA, and a

_{o}is the slope in degrees per mA in the relationship between ocular torsion and visual tilt. T

_{visual}is visual tilt in degrees, and a

_{v}is the slope in degrees per mA in the relationship between visual tilt and vestibular input.

#### 2.4. Exponential Model of Ocular Torsion and Resulting Visual Tilt

_{ocular}is the ocular torsion in degrees, V is the vestibular input in mA, a

_{o}determines the slope of the function (with lower numbers reflecting a steeper slope), and b

_{o}determines the asymptote of the function (preventing T

_{ocular}to ever rise above b

_{o}, regardless of the value of V). T

_{visual}is the visual tilt in degrees, and a

_{v}and b

_{v}have the same purpose as a

_{o}and b

_{o,}but can be of different values.

#### 2.5. Curve Fitting

## 3. Results

#### 3.1. Parameter Estimates

_{o}= 0.483 and b

_{o}= 0.913 for the linear model (Equation (1)), a

_{o}= 0.672 for the directly proportional linear model (Equation (3)), and a

_{o}= 3.722 and b

_{o}= 4.714 for the exponential model (Equation (5)). The best fits for visual tilt were a

_{v}= 1.421 and b

_{v}= 0.000 for the linear model (Equation (2)), a

_{v}= 1.421 in the directly proportional linear model (Equation (4)), and a

_{v}= 3.649 and b

_{v}= 7.00 for the exponential model (Equation (6)).

#### 3.2. Ocular Torsion

#### 3.3. Visual Tilt

#### 3.4. Visual Tilt as a Function of Ocular Torsion

## 4. Discussion

#### 4.1. Central Processing of Vestibular Information

#### 4.2. Alternative Explanations for a Non-Linear Relationship between Vestibular Input and Ocular Torsion

#### 4.3. Vestibular Effects on Attention

## 5. Conclusions

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**(

**A**) When the head is in an upright position, so are the eyes and the visual world. (

**B**) If the eyes were to remain upright with respect to a rolling head, the visual world would tilt. (

**C**) Due to the vestibulo-ocular reflex, the eyes rotate in the opposite direction of the rolling head. This counteracts most of the rotation of the visual field. (

**D**) Some authors have argued that vestibular input is also processed centrally, to directly tilt visual fields.

**Figure 2.**Visualisation of the residual sum of squares in parameter space as a function of the a (x-axis) and b parameter (y-axis) in linear models (Equations (1) and (2); top row, titled ‘lin’), directly proportional linear models (Equations (3) and (4); middle row, titled ‘lin-prop’), and exponential models (Equations (5) and (6); bottom row, titled ‘exp’) of the relationship between galvanic vestibular stimulation and ocular torsion (

**left column**) or visual tilt (

**right column**). Lower values indicate better fits and are indicated by lighter colours. The best fit is indicated by a pink circle.

**Figure 3.**Ocular torsion (blue) and visual tilt (yellow) in degrees (y-axis) as a function of unipolar direct current galvanic vestibular stimulation (x-axis). Solid lines represent the average and shading the standard error of the mean in data reported by Zink et al. (1998). Dotted lines represents directly proportional linear fits (Equations (3) and (4)), and dashed lines represent exponential model fits (Equations (5) and (6)).

**Figure 4.**The relationship between the effects of galvanic vestibular stimulation on ocular torsion (x-axis) and visual tilt (y-axis). Points indicate averages of data reported by Zink et al. (1998) for galvanic vestibular stimulation unipolar direct current intensities 1.5, 2.0, and 3.0 mA, and error bars indicate the standard error of the mean. The dotted line (labelled ‘lin–lin’) is a combination of directly proportional linear models of the relationship between vestibular input and ocular torsion (Equation (3)) or visual tilt (Equation (4)). The dashed line (labelled ‘exp–exp’ is a combination of exponential models of the relationship between vestibular input and ocular torsion (Equation (5)) or visual tilt (Equation (6)). The dashed-dotted line (labelled ‘exp–lin’) represents a combination of Equations (4) and (5). The fits are the same as those presented in Figure 2 and Figure 3; they are simply replotted in the same space.

**Table 1.**Results from Zink et al. (1998), Electroencephalography and Clinical Neurophysiology, 107, pp. 200–205. Zink and colleagues applied unipolar direct current with the anode on the right or left mastoid. They measured ocular torsion and visual tilt in degrees of rotation at different galvanic vestibular stimulation intensities. Results reported by Zink and colleagues (and reprinted here) are the average rotation (unsigned), the standard deviation (between round brackets), the minimum and maximum measured values (between square brackets), and the number of participants tested in a particular cell. Ocular torsion occurred towards the anode, whereas visual tilt occurred away from the anode.

Current Strength | Left Anodal Stimulation | Right Anodal Stimulation | ||
---|---|---|---|---|

(mA) | Ocular Torsion | Visual Tilt | Ocular Torsion | Visual Tilt |

1.0 | 1.0 (0.4) [0.5–1.5] N = 6 | 1.2 (0.3) [0.6–1.4] N = 6 | ||

1.5 | 1.3 (0.1) [1.2–1.4] N = 2 | 2.2 (0.9) [1.3–3.3] N = 4 | 1.4 (0.1) [1.3–1.4] N = 2 | 1.7 (0.5) [1.3–2.3] N = 4 |

2.0 | 2.0 (0.5) [1.3–2.5] N = 7 | 2.6 (1.4) [1.3–6.3] N = 12 | 2.1 (0.5) [1.5–2.8] N = 7 | 2.6 (1.2) [1.0–5.8] N = 12 |

2.5 | 3.2 (2.3) [1.2–9.4] N = 12 | 3.1 (2.0) [1.0–8.5] N = 12 | ||

3.0 | 2.5 (0.8) [1.4–3.5] N = 7 | 4.9 (1.5) [3.0–6.5] N = 4 | 3.0 (0.6) [2.2–3.5] N = 7 | 4.8 (1.8) [2.6–6.4] N = 4 |

4.0 | 2.9 (1.0) [1.2–3.8] N = 6 | 3.3 (1.3) [1.3–4.2] N = 6 | ||

5.0 | 3.2 (1.1) [2.0–4.1] N = 3 | 3.6 (1.9) [1.5–4.3] N = 3 | ||

6.0 | 3.6 (1.3) [2.2–4.5] N = 3 | 4.1 (1.7) [2.2–5.2] N = 3 | ||

7.0 | 3.9 (1.8) [2.6–5.2] N = 2 | 4.0 (2.1) [2.5–5.4] N = 2 |

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**MDPI and ACS Style**

Dalmaijer, E.S. Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability. *Vision* **2018**, *2*, 16.
https://doi.org/10.3390/vision2020016

**AMA Style**

Dalmaijer ES. Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability. *Vision*. 2018; 2(2):16.
https://doi.org/10.3390/vision2020016

**Chicago/Turabian Style**

Dalmaijer, Edwin S. 2018. "Beyond the Vestibulo-Ocular Reflex: Vestibular Input is Processed Centrally to Achieve Visual Stability" *Vision* 2, no. 2: 16.
https://doi.org/10.3390/vision2020016