Neural mechanisms of binocular motion in depth perception Milena Kaestner PhD University of York Psychology May 2018 1 2 Abstract Motion in depth (MID) can be cued by two binocular sources of information. These are changes in retinal disparity over time (changing disparity, CD), and binocular opponent velocity vectors (inter-ocular velocity difference, IOVD). This thesis presents a series of psychophysical and fMRI experiments investigating the neural pathways supporting the perception of CD and IOVD. The first two experiments investigated how CD and IOVD mechanisms draw on information encoded in the magnocellular, parvocellular and koniocellular pathways. The chromaticity of CD and IOVD-isolating stimuli was manipulated to bias activity in these three pathways. Although all stimulus types and chromaticities supported a MID percept, fMRI revealed an especially dominant koniocellular contribution to the IOVD mechanism. Because IOVD depends on eye-specific velocity signals, experiment three sought to identify an area in the brain that encodes motion direction and eye of origin information. Classification and multivariate pattern analysis techniques were applied to fMRI data, but no area where both types of information were present simultaneously was identified. Results suggested that IOVD mechanisms inherit eye-specific information from V1. Finally, experiment four asked whether activity elicited by CD and IOVD stimuli could also be modulated by an attentional task where participants were asked to detect changes in MID or local contrast. fMRI activity was strongly modulated by attentional state, and activity in motion-selective areas was predictive of whether participants correctly identified the change in CD or IOVD MID. This suggests that these areas contain populations of neurons that are crucial for detecting, and behaviourally responding to, both types of MID. The work presented in this thesis detail a thorough investigation of the neural pathways that underlie the computation of CD and IOVD cues to MID. 3 List of Contents Abstract……………………………………………………………………………………………….. 3 List of Contents……………………………………………………………………………………… 4 List of Tables……………………………………………………………………………………..….. 8 List of Figures……………………………………………………………………………………….. 9 Acknowledgements……………………………………………………………………………….. 12 Author’s declaration………………………………………………………………………………..13 Chapter 1. Introduction ................................................................................................... 15 1.1 Fundamentals of visual processing: retina to cortex ........................................ 16 1.1.1 Retinal physiology ........................................................................................... 16 1.1.2 The primary visual pathways: retina to V1 ....................................................... 18 1.2 Binocularity and stereopsis................................................................................. 22 1.3 Stereograms and kinematograms: the separate study of depth and motion ... 24 1.4 Binocular cues to motion in depth perception ................................................... 26 1.4.1 Changing disparity........................................................................................... 26 1.4.2 Inter-ocular velocity difference ......................................................................... 27 1.4.3 Isolating CD and IOVD cues: stimulus design ................................................. 29 1.4.4 Evidence for the CD mechanism ..................................................................... 31 1.4.5 Evidence for the IOVD mechanism .................................................................. 32 1.4.6 Relative contributions of CD and IOVD to 3D motion perception ..................... 34 1.4.7 Spatiotemporal tuning of binocular MID mechanisms ...................................... 35 1.5 Neural encoding of 3D motion ............................................................................. 36 1.5.1 Motion and depth encoding ............................................................................. 36 1.5.2 Cortical and subcortical routes into MT ............................................................ 37 1.5.3 Evidence for MID processing in MT ................................................................. 39 1.6 Summary and outstanding questions ................................................................. 43 1.7 Outline of this thesis ............................................................................................ 44 1.8 Supplementary information ................................................................................. 45 Chapter 2. Chromatic disparity and velocity cues contribute to motion in depth perception ........................................................................................................................ 47 2.1 Abstract ................................................................................................................ 47 2.2 Introduction .......................................................................................................... 48 2.2.1 Binocular cues to motion in depth .................................................................... 48 2.2.2 Chromatic cues to motion perception .............................................................. 50 2.3 Methods ................................................................................................................ 51 4 2.3.1 Participants ...................................................................................................... 51 2.3.2 Materials .......................................................................................................... 52 2.3.3 Stimulus design ............................................................................................... 52 2.3.4 CD stimuli ........................................................................................................ 54 2.3.5 IOVD stimuli .................................................................................................... 55 2.3.6 Participant training ........................................................................................... 55 2.3.7 Procedure ........................................................................................................ 56 2.4 Results .................................................................................................................. 57 2.4.1 Contrast thresholding....................................................................................... 57 2.4.2 Coherence thresholding ................................................................................... 58 2.4.3 Achromatic masking ........................................................................................ 61 2.5 Discussion ............................................................................................................ 62 2.5.1 Chromatic input to MID mechanisms ............................................................... 62 2.5.2 Properties of the CD and IOVD mechanisms ................................................... 64 2.5.3 Conclusions ..................................................................................................... 64 Chapter 3. Distinct response patterns for achromatic and S-cone inputs to cortical motion in depth mechanisms ............................................................................................ 67 3.1 Abstract ................................................................................................................. 67 3.2 Introduction .......................................................................................................... 68 3.3 Materials and methods ......................................................................................... 70 3.3.1 Participants ...................................................................................................... 70 3.3.2 Apparatus ........................................................................................................ 71 3.3.3 Stimulus design ............................................................................................... 72 3.3.4 CD stimulus ..................................................................................................... 73 3.3.5 CD control stimulus ......................................................................................... 74 3.3.6 IOVD stimulus ................................................................................................. 74 3.3.7 IOVD control stimulus ...................................................................................... 75 3.3.8 Isoluminance setting ........................................................................................ 75 3.3.9 MRI parameters ............................................................................................... 76 3.3.10 fMRI procedure and task ................................................................................. 77 3.3.11 Mapping regions of interest ............................................................................. 79 3.3.12 Whole-brain analysis ....................................................................................... 81 3.3.13 ROI analysis .................................................................................................... 82 3.4 Results .................................................................................................................. 83 3.4.1 Whole-brain results .........................................................................................