Update alt text from block preview

Is it possible to update an individual image field, from within a block preview? This is what I have:

panel.plugin("ar/gal-block", {
  blocks: {
    gal: {
      methods: {
       updateSlide(index, field, value) {
          this.content.slides[index][field] = value;
          this.update({ slides: this.content.slides });
        }
      },
    
      template: `
    <template>
    <ul>
      <li v-for="(slide, slideIndex) in content.slides">
       <img class="w-full" v-bind:src=slide.url />
    <k-writer
      :value="slide.alt"
      @input="updateSlide(slideIndex, 'alt', $event)"
    />
    </li>
    </ul>
</template>
    `,
    },
  },
});

{{ slide.alt }} returns nothing, but interestingly {{ slide.info }} does. I could set the info to the alt field, but I guess I can’t update it?