Amazon’s voice-controlled speaker Echo and its Alexa software have been so successful that even rivals such as Google and reportedly Apple are developing competing versions.

But Babak Hodjat, the inventor of the technology behind Apple’s voice recognition system Siri, doesn’t believe in Echo and Alexa’s hype. He thinks they still lack one major component that makes human-machine conversations more complete: visual interactions.

“It has to be augmented with all sorts of other visual cues, interactions, and maybe show some icons to allow the user to be able to click,” Hodjat told Business Insider. “A solely speech recognition based system with no other user interface or contextual elements is incomplete.”

Hodjat, who’s now running Sentient Technologies, an artificial intelligence startup with $135 million in funding, was one of the main inventors of the AI technology that later became the inspirational basis for Siri, according to his LinkedIn page.

He admits he might be a little partial to Siri, but still argues devices that are solely controlled by the voice make the interaction “weaker” and is a “digression” from all the progress the tech industry has made in graphical user interfaces and contextual systems. Instead, Hodjat believes clicking and typing capabilities must be available, and ultimately a camera has to be there to capture the full emotions of the conversation.

Amazon’s Echo, for example, has no screens and is only controlled by the user’s voice. You can play music, make online orders, or get a rundown of daily news headlines by talking to it. Siri, on the other hand, is a similar voice-controlled system but works in conjunction with a screen to visualize the conversation, like showing a 5-day weather forecast.

“Solely speech recognition-based system is only going to address a subset of the needs for ultimate conversational models,” he adds. “Right now, it’s just this little side niche that’s cool and you play around with it.”

Hodjat doesn’t dispute Echo and Alexa are great products. But in his view, there are still lots of shortcomings without a screen to look at.

“Amazon’s done a very good job with Alexa, but I think the screen to augment the interaction is important,” he says.