carrierwave + nested models: file_field not calling "create" method - ruby-on-rails

Question

I am trying to follow Railscast Ep 381 to integrate multi-file upload into my Rails app. For my app, the Projects model has many Steps, and Steps have many Images. The Image model is using a Carrierwave uploader.
Right now, I'm able to upload single image files from within the edit_steps path. But I'm trying to design the upload interface so that a gallery on the edit_steps page automatically refreshes once new images have been added (so once images have been selected but the form has not yet been submitted).
According to the Railscast episode, when you select images, they should automatically call the create action for each file. But my application is clearly not doing that. How can I ensure that the create method of the Image model is being called?
step.rb
class Step < ActiveRecord::Base
extend FriendlyId
friendly_id :number
attr_accessible :description, :name, :number, :project_id, :images_attributes
belongs_to :project
has_many :images
accepts_nested_attributes_for :images, :allow_destroy => :true
end
image.rb
class Image < ActiveRecord::Base
attr_accessible :project_id, :step_id, :file, :caption
belongs_to :step
belongs_to :project
mount_uploader :file, FileUploader
end
views/steps/edit.html.erb
%= semantic_form_for [#project, #step], :html => {:multipart => true} do |f| %>
<%= f.inputs do%>
....
<div id="images">
<%= render :partial => 'images/image', :collection => #step.images.all %>
</div>
<div class="clear"></div>
....
<%= f.fields_for :images, Image.new do |image_form| %>
<%= image_form.file_field :file, multiple: true, name: "image[file]"%>
<%end%>
javascript/images.js.coffee
jQuery ->
$('#new_image').fileupload
dataType: "script"
controllers/images.controller
def create
#image = Image.create(params[:image])
end
images/create.js.erb
<% if #image.new_record? %>
alert("Failed to upload image: <%= j #image.errors.full_messages.join(', ').html_safe %>");
<% else %>
alert("adding images")
$("#images").append("<%= j render(#image) %>");
<% end %>