A portable display device comprising: an optically transparent sheet comprising an electrically conductive layer; an electrode element that is electrically connected to the optically transparent sheet; and electro-vibration circuitry connected to the electrically conductive layer and the electrode element, in use the electro-vibration circuitry being configured to provide a time-varying voltage signal across the electrically conductive layer and the electrode element so as to cause a user to experience electro-vibration in a first body part of the user when the first body part is moved across an exterior surface of the optically transparent sheet while a second body part of the user is in contact with the electrode element; and a display panel configured to display one or more objects to the user, wherein the optically transparent sheet is arranged to overlie at least a portion of a display surface of the display panel, and the electrode element constitutes all or a part of a housing of the portable display device; the portable display device further configured to determine whether a location of a touch input on the optically transparent sheet is equal to a location of one of the one or more objects displayed on the display panel; and the electro-vibration circuitry configured to switch on the voltage signal when it is determined that the location of the touch input is equal to the location of one of the one or more objects displayed on the display panel; wherein the display surface constitutes a portion of a front exterior surface of the device and wherein the electrode element is provided on a rear exterior surface of the device. an optically transparent sheet comprising an electrically conductive layer; an electrode element that is electrically connected to the optically transparent sheet; and electro-vibration circuitry connected to the electrically conductive layer and the electrode element, in use the electro-vibration circuitry being configured to provide a time-varying voltage signal across the electrically conductive layer and the electrode element so as to cause a user to experience electro-vibration in a first body part of the user when the first body part is moved across an exterior surface of the optically transparent sheet while a second body part of the user is in contact with the electrode element; and a display panel configured to display one or more objects to the user, wherein the optically transparent sheet is arranged to overlie at least a portion of a display surface of the display panel, and the electrode element constitutes all or a part of a housing of the portable display device; the portable display device further configured to determine whether a location of a touch input on the optically transparent sheet is equal to a location of one of the one or more objects displayed on the display panel; and the electro-vibration circuitry configured to switch on the voltage signal when it is determined that the location of the touch input is equal to the location of one of the one or more objects displayed on the display panel; wherein the display surface constitutes a portion of a front exterior surface of the device and wherein the electrode element is provided on a rear exterior surface of the device.