Accessibility - Screen reader only reading alt text, not slide text

Hello all,

I was using the IE Narrator and NVDA to test out a module I created in Storyline and loaded on Moodle, and though it reads out the header once it reaches the text boxes it ready out the alt text, but not the text box content. So for example I've set the alt text as 'slide instructions', and rather than reading out what the instructions are I only hear 'slide instructions'. 

Is there a simple fox for this, or am I doing something incorrectly?