Multiple file upload validation in laravel

I have multiple input fields with multiple file upload for each field.

<?php for ($i = 0; $i < $total; $i++)
   {
?>
<div class="col-md-3 addedClass">
     <label>Vehicle Images</label>
     <input type="file" name="vehicle_image[{{$i}}][]" multiple="multiple">
     @if($errors->has('vehicle_image'))
          <span class="help-block">
              <strong>{{$errors->first('vehicle_image')}}</strong>
          </span>
     @endif
</div>
<?php } ?>

I have got files in the request like this:

"vehicle_image" => array:2 [▼
    0 => array:2 [▼
      0 => "citizenship.jpg"
      1 => "logo_vehicle.png"
    ]
    1 => array:2 [▼
      0 => "ae backend.jpg"
      1 => "logo_vehicle.png"
    ]
  ]

In this case, I have two input fields with 2/2 files. When I have tried to validate mime type for only images like this:

$this->validate($request,[
           'vehicle_image' => 'mimes:jpeg,png,bmp,tiff |max:4096'
       ],$messages[
            // error messages 
      ]);

I have got following error:

FatalThrowableError in ReservationController.php line 67: Cannot use [] for reading

Can someone tell me what is wrong with the above code ? Suggestions are appreciated.