You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spm_eeg_inv_visu3D_api.m
    path of file: ./repos/spm
    
    the code of the file until where you have to start completion: function varargout = spm_eeg_inv_visu3D_api(varargin)
% SPM_EEG_INV_VISU3D_API M-file for spm_eeg_inv_visu3D_api.fig
% - FIG = SPM_EEG_INV_VISU3D_API launch spm_eeg_inv_visu3D_api GUI.
% - D   = SPM_EEG_INV_VISU3D_API(D) open with D
% - SPM_EEG_INV_VISU3D_API(filename) where filename is the eeg/meg .mat file
% - SPM_EEG_INV_VISU3D_API('callback_name', ...) invoke the named callback.
%
% Last Modified by GUIDE v2.5 18-Feb-2011 14:23:27
%__________________________________________________________________________

% Jeremie Mattout
% Copyright (C) 2008-2022 Wellcome Centre for Human Neuroimaging


% INITIALISATION CODE
%--------------------------------------------------------------------
    
function LoadData_Callback(hObject, eventdata, handles)
S         = spm_select(1, '.mat', 'Select EEG/MEG mat file');
handles.D = spm_eeg_load(S);
spm_eeg_inv_visu3D_api_OpeningFcn(hObject, [], handles);


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ACTIVITY TO DISPLAY
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% --- Executes on selection change in Activity.
function Activity_Callback(hObject, eventdata, handles)
ActToDisp = get(handles.Activity,'Value');
if ActToDisp == 1
    set(handles.checkbox_absv,   'Enable','on');
    set(handles.checkbox_norm,   'Enable','on');
    set(handles.slider_time,     'Enable','on');
    set(handles.time_bin,        'Enable','on');
else
    set(handles.checkbox_norm,   'Enable','off');
    set(handles.slider_time,     'Enable','off');
    set(handles.time_bin,        'Enable','off');
end