conditional logic dynamically populated field

Hi, I am dynamically populating a text field with a value from a drop down. I was hoping that the value would initiate some conditional logic to show/hide form fields, however it doesn't seem as though the conditional logic registers when that field has a value written to it.

To write the value I am using:
jQuery("#input_4_64").val(selectedValue);
This inserts the value into that field and it writes correctly but it doesn't fire the logic unless I manually input the "condition".

Is there a way around this? or to make the conditional logic to "see" when that value changes/gets written?

I am not sure how I would do that--well, I can see how to do that, but writing individual conditions would make a very long set of conditional logic and not be quite as dynamic as I am hoping for--the drop down is generated from a Taxonomy. I was hoping to utilize this "filter" I have written

This is what I am working with:

add_filter("gform_pre_render_4", "monitor_dropdown");
function monitor_dropdown($form){

?>
    <script type="text/javascript">

    jQuery(document).ready(function(){

      jQuery('#input_4_40').bind('change', function()
        {

           //get selected value from drop down;
            var selectedValue = jQuery("#input_4_40").val();

            //populate a text field with the selected drop down value
            jQuery("#input_4_64").val(selectedValue);

       });

    });

$(function(){
var groupFromValue = {

227: {
        name: 'B-1300SS',
        group: '8'
    },

228: {
        name: 'B-1500SS',
        group: '3'
    },

  235: {
        name: 'SG4600-72',
        group: '9'
}

}

$('select').change(function() {
    var machineName = groupFromValue[$(this).val()].name;
    var machineGroup = groupFromValue[$(this).val()].group;
	jQuery("#input_4_63").val(machineName);
	jQuery("#input_4_62").val(machineGroup);

});
});
    </script>
<?php

return $form;
}

I filter the value and name to come up with group. based on teh data input into the field (in this case (machineGroup) i am trying to use that value to trigger a few input fields on the form. I am doing it this way because i have over 50 machines which are sorted into 3 machineGroup

For anyone else looking for a similar answer:
You can manually fire the change event after you dynamically populate the field, eg:

jQuery("#input_4_62").val(machineGroup).change();