validate_on_update not highlighting fields

I am using the following is a sample validate_on_update action in my
model:

validate_on_update
  if internet_access == "Y"
    if internet_use.blank?
      errors.add_to_base("Please describe your internet use.")
    end
  end
end

This successfully throws the validation error if internet access is
checked and internet use is left blank, however it does not properly
highlight the field that was left blank (in this case "internet_use").
Any suggestions?

When you use add_to_base method, it adds it to the base of the form,
not a specific field.

You can add the error to the internet_use field:

errors.add(:internet_use, "Please describe your internet use.")