ng-change method not executing - angularjs

Question

I'm trying to pass the object selected in a to update the data of another object.
Here is the html
<select id="categoryListBox"
ng-model="category.selected"
ng-change="updateCategory(category.selected)"
ng-options="category._id as category.name for category in categories">
</select>
This renders
<select id="categoryListBox"
ng-model="category.selected"
ng-change="updateCategory()"
ng-options="category._id as category.name for category in categories"
class="ng-valid ng-dirty">
<option value="0" selected="selected">Test4</option>
<option value="1">Test5</option>
</select>
Here is my update function
$scope.updateCategory = function(){
console.log('hi');
}
My problem is that right now when the selected item changes the updateCategory method doesn't fires. I would like for whenever the option selected in the <select></select> changes that my $scope.updateCategory method fires. It would also be awesome if I could pass the category selected to this method.
Update here is the my initalization which populates the array categories
$scope.init = function (){
console.log('dfakjsdhf');
console.log(apiUrl);
$scope.category = {};
$scope.subcategory = {};
//$scope.categories = {_id: 1, name:'test'};
$http({ method: 'GET', url: apiUrl + '/categories'}).
success(function (data, status, headers, config) {
$scope.categories = data;
console.log($scope.categories);
}).
error(function (data, status, headers, config) {
console.log('error');
});
};

Answer 1

Just rename your ng-model from category.selected to something else. As per my understanding, In your code there is an ambiguity between ng-options category and ng-model category
<select id="categoryListBox"
ng-model="categorymodel"
ng-change="updateCategory(categorymodel)"
ng-options="category.id as category.name for category in categories">
</select>
DEMO

Answer 2

There is no need to pass the category.selected in your function. In your js controller it will be there in your scope, just use it in your updateCategory() function.
JSFiddle
Html:
<select id="categoryListBox"
ng-model="category.selected"
ng-change="updateCategory()"
ng-options="category.id as category.name for category in categories">
</select>
JS:
$scope.updateCategory = function(){
alert($scope.category.selected);
}